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Table of Contents

Preface

The Spring Data for Apache Cassandra project applies core Spring concepts to the development of solutions using the Cassandra Columnar data store. A "template" is provided as a high-level abstraction for storing and querying documents. You will notice similarities to the JDBC support in the core Spring Framework.

This document is the reference guide for Spring Data support for Cassandra. It explains Cassandra module concepts, semantics and the syntax for various stores namespaces.

This section provides a basic introduction to Spring, Spring Data and the Cassandra database. The rest of the document refers only to Spring Data for Apache Cassandra features and assumes the user is familiar with Cassandra as well as core Spring concepts.

1. Knowing Spring

Spring Data uses the Spring Framework’s core functionality, such as the IoC container, validation, type conversion and data binding, expression language, AOP, JMX integration, DAO support, and specifically the DAO Exception Hierarchy.

While it is not important to know the Spring APIs, understanding the concepts behind them is. At a minimum, the idea behind IoC should be familiar no matter what IoC container you choose to use.

The core functionality of the Cassandra support can be used directly, with no need to invoke the IoC services of the Spring container. This is much like JdbcTemplate, which can be used 'standalone' without any other services of the Spring container. To leverage all the features of Spring Data for Apache Cassandra, such as the repository support, you will need to configure some parts of the library using Spring.

To learn more about Spring, you can refer to the comprehensive (and sometimes disarming) documentation that explains in detail the Spring Framework. There are a lot of articles, blog entries and books on the matter. Take a look at the Spring Framework home page for more information.

2. Knowing NoSQL and Cassandra

NoSQL stores have taken the storage world by storm. It is a vast domain with a plethora of solutions, terms and patterns (to make things worse, even the term itself has multiple meanings). While some of the principles are common, it is crucial that the user is familiar to some degree with the Cassandra Columnar NoSQL Datastore supported by Spring Data for Apache Cassandra. The best way to get acquainted with Cassandra is to read the documentation and follow the examples. It usually doesn’t take more then 5-10 minutes to go through them and if you are coming from a RDBMS background, many times these exercises can be an eye opener.

The starting ground for learning about Cassandra is cassandra.apache.org. Also, here is a list of other useful resources:

3. Requirements

Spring Data for Apache Cassandra 1.x binaries require JDK level 6.0 and above, and Spring Framework 5.0.0.RC2 and above.

In terms of Cassandra at least 2.0.

4. Additional Help Resources

Learning a new framework is not always straight forward. In this section, we try to provide what we think is an easy to follow guide for starting with Spring Data for Apache Cassandra module. However, if you encounter issues or you are just looking for an advice, feel free to use one of the links below:

4.1. Support

There are a few support options available:

4.1.1. Community Forum

Spring Data on Stackoverflow is a tag for all Spring Data (not just Cassandra) users to share information and help each other. Note that registration is needed only for posting.

Developers post questions and answers on . The two key tags to search for related answers to this project are:

4.1.2. Professional Support

Professional, from-the-source support, with guaranteed response time, is available from Pivotal Sofware, Inc., the company behind Spring Data and Spring.

4.2. Following Development

For information on the Spring Data for Apache Cassandra source code repository, nightly builds and snapshot artifacts please see the Spring Data for Apache Cassandra homepage. You can help make Spring Data best serve the needs of the Spring community by interacting with developers through the Community on Stackoverflow. To follow developer activity look for the mailing list information on the Spring Data for Apache Cassandra homepage. If you encounter a bug or want to suggest an improvement, please create a ticket on the Spring Data issue tracker. To stay up to date with the latest news and announcements in the Spring eco system, subscribe to the Spring Community Portal. Lastly, you can follow the Spring blog or the project team on Twitter (SpringData).

4.3. Project Metadata

5. New & Noteworthy

5.1. What’s new in Spring Data for Apache Cassandra 2.0

  • Update and Query objects.

  • CRUD repository interface renaming: CassandraRepository using MapId is now renamed to MapIdCassandraRepository. TypedIdCassandraRepository is renamed to CassandraRepository.

  • Lightweight transactions via InsertOptions and UpdateOptions using the Template API.

5.2. What’s new in Spring Data for Apache Cassandra 1.5

  • Assert compatibility with Cassandra 3.0 and Cassandra Java Driver 3.0.

  • Configurable ProtocolVersion and QueryOptions on Cluster level.

  • Support for Optional as query method result and argument.

  • Declarative query methods using query derivation

  • Support for User-Defined types and mapped User-Defined types using @UserDefinedType.

  • The following annotations have been enabled to build own, composed annotations: @Table, @UserDefinedType, @PrimaryKey, @PrimaryKeyClass, @PrimaryKeyColumn, @Column, @Query, @CassandraType.

6. Dependencies

Due to different inception dates of individual Spring Data modules, most of them carry different major and minor version numbers. The easiest way to find compatible ones is by relying on the Spring Data Release Train BOM we ship with the compatible versions defined. In a Maven project you’d declare this dependency in the <dependencyManagement /> section of your POM:

Example 1. Using the Spring Data release train BOM
<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-releasetrain</artifactId>
      <version>${release-train}</version>
      <scope>import</scope>
      <type>pom</type>
    </dependency>
  </dependencies>
</dependencyManagement>

The current release train version is Kay-M4. The train names are ascending alphabetically and currently available ones are listed here. The version name follows the following pattern: ${name}-${release} where release can be one of the following:

  • BUILD-SNAPSHOT - current snapshots

  • M1, M2 etc. - milestones

  • RC1, RC2 etc. - release candidates

  • RELEASE - GA release

  • SR1, SR2 etc. - service releases

A working example of using the BOMs can be found in our Spring Data examples repository. If that’s in place declare the Spring Data modules you’d like to use without a version in the <dependencies /> block.

Example 2. Declaring a dependency to a Spring Data module
<dependencies>
  <dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-jpa</artifactId>
  </dependency>
<dependencies>

6.1. Dependency management with Spring Boot

Spring Boot already selects a very recent version of Spring Data modules for you. In case you want to upgrade to a newer version nonetheless, simply configure the property spring-data-releasetrain.version to the train name and iteration you’d like to use.

6.2. Spring Framework

The current version of Spring Data modules require Spring Framework in version 5.0.0.RC2 or better. The modules might also work with an older bugfix version of that minor version. However, using the most recent version within that generation is highly recommended.

7. Working with Spring Data Repositories

The goal of Spring Data repository abstraction is to significantly reduce the amount of boilerplate code required to implement data access layers for various persistence stores.

Spring Data repository documentation and your module

This chapter explains the core concepts and interfaces of Spring Data repositories. The information in this chapter is pulled from the Spring Data Commons module. It uses the configuration and code samples for the Java Persistence API (JPA) module. Adapt the XML namespace declaration and the types to be extended to the equivalents of the particular module that you are using. Namespace reference covers XML configuration which is supported across all Spring Data modules supporting the repository API, Repository query keywords covers the query method keywords supported by the repository abstraction in general. For detailed information on the specific features of your module, consult the chapter on that module of this document.

7.1. Core concepts

The central interface in Spring Data repository abstraction is Repository (probably not that much of a surprise). It takes the domain class to manage as well as the id type of the domain class as type arguments. This interface acts primarily as a marker interface to capture the types to work with and to help you to discover interfaces that extend this one. The CrudRepository provides sophisticated CRUD functionality for the entity class that is being managed.

Example 3. CrudRepository interface
public interface CrudRepository<T, ID extends Serializable>
    extends Repository<T, ID> {

    <S extends T> S save(S entity); (1)

    T findOne(ID primaryKey);       (2)

    Iterable<T> findAll();          (3)

    Long count();                   (4)

    void delete(T entity);          (5)

    boolean exists(ID primaryKey);  (6)

    // … more functionality omitted.
}
1 Saves the given entity.
2 Returns the entity identified by the given id.
3 Returns all entities.
4 Returns the number of entities.
5 Deletes the given entity.
6 Indicates whether an entity with the given id exists.
We also provide persistence technology-specific abstractions like e.g. JpaRepository or MongoRepository. Those interfaces extend CrudRepository and expose the capabilities of the underlying persistence technology in addition to the rather generic persistence technology-agnostic interfaces like e.g. CrudRepository.

On top of the CrudRepository there is a PagingAndSortingRepository abstraction that adds additional methods to ease paginated access to entities:

Example 4. PagingAndSortingRepository
public interface PagingAndSortingRepository<T, ID extends Serializable>
  extends CrudRepository<T, ID> {

  Iterable<T> findAll(Sort sort);

  Page<T> findAll(Pageable pageable);
}

Accessing the second page of User by a page size of 20 you could simply do something like this:

PagingAndSortingRepository<User, Long> repository = // … get access to a bean
Page<User> users = repository.findAll(new PageRequest(1, 20));

In addition to query methods, query derivation for both count and delete queries, is available.

Example 5. Derived Count Query
public interface UserRepository extends CrudRepository<User, Long> {

  Long countByLastname(String lastname);
}
Example 6. Derived Delete Query
public interface UserRepository extends CrudRepository<User, Long> {

  Long deleteByLastname(String lastname);

  List<User> removeByLastname(String lastname);

}

7.2. Query methods

Standard CRUD functionality repositories usually have queries on the underlying datastore. With Spring Data, declaring those queries becomes a four-step process:

  1. Declare an interface extending Repository or one of its subinterfaces and type it to the domain class and ID type that it will handle.

    interface PersonRepository extends Repository<Person, Long> { … }

  2. Declare query methods on the interface.

    interface PersonRepository extends Repository<Person, Long> {
  List<Person> findByLastname(String lastname);
}

  3. Set up Spring to create proxy instances for those interfaces. Either via JavaConfig:

    import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

@EnableJpaRepositories
class Config {}

    or via XML configuration:

    <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:jpa="http://www.springframework.org/schema/data/jpa"
   xsi:schemaLocation="http://www.springframework.org/schema/beans
     http://www.springframework.org/schema/beans/spring-beans.xsd
     http://www.springframework.org/schema/data/jpa
     http://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

   <jpa:repositories base-package="com.acme.repositories"/>

</beans>

    The JPA namespace is used in this example. If you are using the repository abstraction for any other store, you need to change this to the appropriate namespace declaration of your store module which should be exchanging jpa in favor of, for example, mongodb.

    Also, note that the JavaConfig variant doesn’t configure a package explictly as the package of the annotated class is used by default. To customize the package to scan use one of the basePackage… attribute of the data-store specific repository @Enable…-annotation.

  4. Get the repository instance injected and use it.

    public class SomeClient {

  @Autowired
  private PersonRepository repository;

  public void doSomething() {
    List<Person> persons = repository.findByLastname("Matthews");
  }
}

The sections that follow explain each step in detail.

7.3. Defining repository interfaces

As a first step you define a domain class-specific repository interface. The interface must extend Repository and be typed to the domain class and an ID type. If you want to expose CRUD methods for that domain type, extend CrudRepository instead of Repository.

7.3.1. Fine-tuning repository definition

Typically, your repository interface will extend Repository, CrudRepository or PagingAndSortingRepository. Alternatively, if you do not want to extend Spring Data interfaces, you can also annotate your repository interface with @RepositoryDefinition. Extending CrudRepository exposes a complete set of methods to manipulate your entities. If you prefer to be selective about the methods being exposed, simply copy the ones you want to expose from CrudRepository into your domain repository.

This allows you to define your own abstractions on top of the provided Spring Data Repositories functionality.
Example 7. Selectively exposing CRUD methods
@NoRepositoryBean
interface MyBaseRepository<T, ID extends Serializable> extends Repository<T, ID> {

  T findOne(ID id);

  T save(T entity);
}

interface UserRepository extends MyBaseRepository<User, Long> {
  User findByEmailAddress(EmailAddress emailAddress);
}

In this first step you defined a common base interface for all your domain repositories and exposed findOne(…) as well as save(…).These methods will be routed into the base repository implementation of the store of your choice provided by Spring Data ,e.g. in the case if JPA SimpleJpaRepository, because they are matching the method signatures in CrudRepository. So the UserRepository will now be able to save users, and find single ones by id, as well as triggering a query to find Users by their email address.

Note, that the intermediate repository interface is annotated with @NoRepositoryBean. Make sure you add that annotation to all repository interfaces that Spring Data should not create instances for at runtime.

7.3.2. Using Repositories with multiple Spring Data modules

Using a unique Spring Data module in your application makes things simple hence, all repository interfaces in the defined scope are bound to the Spring Data module. Sometimes applications require using more than one Spring Data module. In such case, it’s required for a repository definition to distinguish between persistence technologies. Spring Data enters strict repository configuration mode because it detects multiple repository factories on the class path. Strict configuration requires details on the repository or the domain class to decide about Spring Data module binding for a repository definition:

  1. If the repository definition extends the module-specific repository, then it’s a valid candidate for the particular Spring Data module.

  2. If the domain class is annotated with the module-specific type annotation, then it’s a valid candidate for the particular Spring Data module. Spring Data modules accept either 3rd party annotations (such as JPA’s @Entity) or provide own annotations such as @Document for Spring Data MongoDB/Spring Data Elasticsearch.

Example 8. Repository definitions using Module-specific Interfaces
interface MyRepository extends JpaRepository<User, Long> { }

@NoRepositoryBean
interface MyBaseRepository<T, ID extends Serializable> extends JpaRepository<T, ID> {
  …
}

interface UserRepository extends MyBaseRepository<User, Long> {
  …
}

MyRepository and UserRepository extend JpaRepository in their type hierarchy. They are valid candidates for the Spring Data JPA module.

Example 9. Repository definitions using generic Interfaces
interface AmbiguousRepository extends Repository<User, Long> {
 …
}

@NoRepositoryBean
interface MyBaseRepository<T, ID extends Serializable> extends CrudRepository<T, ID> {
  …
}

interface AmbiguousUserRepository extends MyBaseRepository<User, Long> {
  …
}

AmbiguousRepository and AmbiguousUserRepository extend only Repository and CrudRepository in their type hierarchy. While this is perfectly fine using a unique Spring Data module, multiple modules cannot distinguish to which particular Spring Data these repositories should be bound.

Example 10. Repository definitions using Domain Classes with Annotations
interface PersonRepository extends Repository<Person, Long> {
 …
}

@Entity
public class Person {
  …
}

interface UserRepository extends Repository<User, Long> {
 …
}

@Document
public class User {
  …
}

PersonRepository references Person which is annotated with the JPA annotation @Entity so this repository clearly belongs to Spring Data JPA. UserRepository uses User annotated with Spring Data MongoDB’s @Document annotation.

Example 11. Repository definitions using Domain Classes with mixed Annotations
interface JpaPersonRepository extends Repository<Person, Long> {
 …
}

interface MongoDBPersonRepository extends Repository<Person, Long> {
 …
}

@Entity
@Document
public class Person {
  …
}

This example shows a domain class using both JPA and Spring Data MongoDB annotations. It defines two repositories, JpaPersonRepository and MongoDBPersonRepository. One is intended for JPA and the other for MongoDB usage. Spring Data is no longer able to tell the repositories apart which leads to undefined behavior.

Repository type details and identifying domain class annotations are used for strict repository configuration identify repository candidates for a particular Spring Data module. Using multiple persistence technology-specific annotations on the same domain type is possible to reuse domain types across multiple persistence technologies, but then Spring Data is no longer able to determine a unique module to bind the repository.

The last way to distinguish repositories is scoping repository base packages. Base packages define the starting points for scanning for repository interface definitions which implies to have repository definitions located in the appropriate packages. By default, annotation-driven configuration uses the package of the configuration class. The base package in XML-based configuration is mandatory.

Example 12. Annotation-driven configuration of base packages
@EnableJpaRepositories(basePackages = "com.acme.repositories.jpa")
@EnableMongoRepositories(basePackages = "com.acme.repositories.mongo")
interface Configuration { }

7.4. Defining query methods

The repository proxy has two ways to derive a store-specific query from the method name. It can derive the query from the method name directly, or by using a manually defined query. Available options depend on the actual store. However, there’s got to be a strategy that decides what actual query is created. Let’s have a look at the available options.

7.4.1. Query lookup strategies

The following strategies are available for the repository infrastructure to resolve the query. You can configure the strategy at the namespace through the query-lookup-strategy attribute in case of XML configuration or via the queryLookupStrategy attribute of the Enable${store}Repositories annotation in case of Java config. Some strategies may not be supported for particular datastores.

  • CREATE attempts to construct a store-specific query from the query method name. The general approach is to remove a given set of well-known prefixes from the method name and parse the rest of the method. Read more about query construction in Query creation.

  • USE_DECLARED_QUERY tries to find a declared query and will throw an exception in case it can’t find one. The query can be defined by an annotation somewhere or declared by other means. Consult the documentation of the specific store to find available options for that store. If the repository infrastructure does not find a declared query for the method at bootstrap time, it fails.

  • CREATE_IF_NOT_FOUND (default) combines CREATE and USE_DECLARED_QUERY. It looks up a declared query first, and if no declared query is found, it creates a custom method name-based query. This is the default lookup strategy and thus will be used if you do not configure anything explicitly. It allows quick query definition by method names but also custom-tuning of these queries by introducing declared queries as needed.

7.4.2. Query creation

The query builder mechanism built into Spring Data repository infrastructure is useful for building constraining queries over entities of the repository. The mechanism strips the prefixes find…By, read…By, query…By, count…By, and get…By from the method and starts parsing the rest of it. The introducing clause can contain further expressions such as a Distinct to set a distinct flag on the query to be created. However, the first By acts as delimiter to indicate the start of the actual criteria. At a very basic level you can define conditions on entity properties and concatenate them with And and Or.

Example 13. Query creation from method names
public interface PersonRepository extends Repository<User, Long> {

  List<Person> findByEmailAddressAndLastname(EmailAddress emailAddress, String lastname);

  // Enables the distinct flag for the query
  List<Person> findDistinctPeopleByLastnameOrFirstname(String lastname, String firstname);
  List<Person> findPeopleDistinctByLastnameOrFirstname(String lastname, String firstname);

  // Enabling ignoring case for an individual property
  List<Person> findByLastnameIgnoreCase(String lastname);
  // Enabling ignoring case for all suitable properties
  List<Person> findByLastnameAndFirstnameAllIgnoreCase(String lastname, String firstname);

  // Enabling static ORDER BY for a query
  List<Person> findByLastnameOrderByFirstnameAsc(String lastname);
  List<Person> findByLastnameOrderByFirstnameDesc(String lastname);
}

The actual result of parsing the method depends on the persistence store for which you create the query. However, there are some general things to notice.

  • The expressions are usually property traversals combined with operators that can be concatenated. You can combine property expressions with AND and OR. You also get support for operators such as Between, LessThan, GreaterThan, Like for the property expressions. The supported operators can vary by datastore, so consult the appropriate part of your reference documentation.

  • The method parser supports setting an IgnoreCase flag for individual properties (for example, findByLastnameIgnoreCase(…)) or for all properties of a type that support ignoring case (usually String instances, for example, findByLastnameAndFirstnameAllIgnoreCase(…)). Whether ignoring cases is supported may vary by store, so consult the relevant sections in the reference documentation for the store-specific query method.

  • You can apply static ordering by appending an OrderBy clause to the query method that references a property and by providing a sorting direction (Asc or Desc). To create a query method that supports dynamic sorting, see Special parameter handling.

7.4.3. Property expressions

Property expressions can refer only to a direct property of the managed entity, as shown in the preceding example. At query creation time you already make sure that the parsed property is a property of the managed domain class. However, you can also define constraints by traversing nested properties. Assume a Person has an Address with a ZipCode. In that case a method name of

List<Person> findByAddressZipCode(ZipCode zipCode);

creates the property traversal x.address.zipCode. The resolution algorithm starts with interpreting the entire part (AddressZipCode) as the property and checks the domain class for a property with that name (uncapitalized). If the algorithm succeeds it uses that property. If not, the algorithm splits up the source at the camel case parts from the right side into a head and a tail and tries to find the corresponding property, in our example, AddressZip and Code. If the algorithm finds a property with that head it takes the tail and continue building the tree down from there, splitting the tail up in the way just described. If the first split does not match, the algorithm move the split point to the left (Address, ZipCode) and continues.

Although this should work for most cases, it is possible for the algorithm to select the wrong property. Suppose the Person class has an addressZip property as well. The algorithm would match in the first split round already and essentially choose the wrong property and finally fail (as the type of addressZip probably has no code property).

To resolve this ambiguity you can use _ inside your method name to manually define traversal points. So our method name would end up like so:

List<Person> findByAddress_ZipCode(ZipCode zipCode);

As we treat underscore as a reserved character we strongly advise to follow standard Java naming conventions (i.e. not using underscores in property names but camel case instead).

7.4.4. Special parameter handling

To handle parameters in your query you simply define method parameters as already seen in the examples above. Besides that the infrastructure will recognize certain specific types like Pageable and Sort to apply pagination and sorting to your queries dynamically.

Example 14. Using Pageable, Slice and Sort in query methods
Page<User> findByLastname(String lastname, Pageable pageable);

Slice<User> findByLastname(String lastname, Pageable pageable);

List<User> findByLastname(String lastname, Sort sort);

List<User> findByLastname(String lastname, Pageable pageable);

The first method allows you to pass an org.springframework.data.domain.Pageable instance to the query method to dynamically add paging to your statically defined query. A Page knows about the total number of elements and pages available. It does so by the infrastructure triggering a count query to calculate the overall number. As this might be expensive depending on the store used, Slice can be used as return instead. A Slice only knows about whether there’s a next Slice available which might be just sufficient when walking through a larger result set.

Sorting options are handled through the Pageable instance too. If you only need sorting, simply add an org.springframework.data.domain.Sort parameter to your method. As you also can see, simply returning a List is possible as well. In this case the additional metadata required to build the actual Page instance will not be created (which in turn means that the additional count query that would have been necessary not being issued) but rather simply restricts the query to look up only the given range of entities.

To find out how many pages you get for a query entirely you have to trigger an additional count query. By default this query will be derived from the query you actually trigger.

7.4.5. Limiting query results

The results of query methods can be limited via the keywords first or top, which can be used interchangeably. An optional numeric value can be appended to top/first to specify the maximum result size to be returned. If the number is left out, a result size of 1 is assumed.

Example 15. Limiting the result size of a query with Top and First
User findFirstByOrderByLastnameAsc();

User findTopByOrderByAgeDesc();

Page<User> queryFirst10ByLastname(String lastname, Pageable pageable);

Slice<User> findTop3ByLastname(String lastname, Pageable pageable);

List<User> findFirst10ByLastname(String lastname, Sort sort);

List<User> findTop10ByLastname(String lastname, Pageable pageable);

The limiting expressions also support the Distinct keyword. Also, for the queries limiting the result set to one instance, wrapping the result into an Optional is supported.

If pagination or slicing is applied to a limiting query pagination (and the calculation of the number of pages available) then it is applied within the limited result.

Note that limiting the results in combination with dynamic sorting via a Sort parameter allows to express query methods for the 'K' smallest as well as for the 'K' biggest elements.

7.4.6. Streaming query results

The results of query methods can be processed incrementally by using a Java 8 Stream<T> as return type. Instead of simply wrapping the query results in a Stream data store specific methods are used to perform the streaming.

Example 16. Stream the result of a query with Java 8 Stream<T>
@Query("select u from User u")
Stream<User> findAllByCustomQueryAndStream();

Stream<User> readAllByFirstnameNotNull();

@Query("select u from User u")
Stream<User> streamAllPaged(Pageable pageable);
A Stream potentially wraps underlying data store specific resources and must therefore be closed after usage. You can either manually close the Stream using the close() method or by using a Java 7 try-with-resources block.
Example 17. Working with a Stream<T> result in a try-with-resources block
try (Stream<User> stream = repository.findAllByCustomQueryAndStream()) {
  stream.forEach(…);
}
Not all Spring Data modules currently support Stream<T> as a return type.

7.4.7. Async query results

Repository queries can be executed asynchronously using Spring’s asynchronous method execution capability. This means the method will return immediately upon invocation and the actual query execution will occur in a task that has been submitted to a Spring TaskExecutor.

@Async
Future<User> findByFirstname(String firstname);               (1)

@Async
CompletableFuture<User> findOneByFirstname(String firstname); (2)

@Async
ListenableFuture<User> findOneByLastname(String lastname);    (3)
1 Use java.util.concurrent.Future as return type.
2 Use a Java 8 java.util.concurrent.CompletableFuture as return type.
3 Use a org.springframework.util.concurrent.ListenableFuture as return type.

7.5. Creating repository instances

In this section you create instances and bean definitions for the repository interfaces defined. One way to do so is using the Spring namespace that is shipped with each Spring Data module that supports the repository mechanism although we generally recommend to use the Java-Config style configuration.

7.5.1. XML configuration

Each Spring Data module includes a repositories element that allows you to simply define a base package that Spring scans for you.

Example 18. Enabling Spring Data repositories via XML
<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns:beans="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://www.springframework.org/schema/data/jpa"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/jpa
    http://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

  <repositories base-package="com.acme.repositories" />

</beans:beans>

In the preceding example, Spring is instructed to scan com.acme.repositories and all its sub-packages for interfaces extending Repository or one of its sub-interfaces. For each interface found, the infrastructure registers the persistence technology-specific FactoryBean to create the appropriate proxies that handle invocations of the query methods. Each bean is registered under a bean name that is derived from the interface name, so an interface of UserRepository would be registered under userRepository. The base-package attribute allows wildcards, so that you can define a pattern of scanned packages.

Using filters

By default the infrastructure picks up every interface extending the persistence technology-specific Repository sub-interface located under the configured base package and creates a bean instance for it. However, you might want more fine-grained control over which interfaces bean instances get created for. To do this you use <include-filter /> and <exclude-filter /> elements inside <repositories />. The semantics are exactly equivalent to the elements in Spring’s context namespace. For details, see Spring reference documentation on these elements.

For example, to exclude certain interfaces from instantiation as repository, you could use the following configuration:

Example 19. Using exclude-filter element
<repositories base-package="com.acme.repositories">
  <context:exclude-filter type="regex" expression=".*SomeRepository" />
</repositories>

This example excludes all interfaces ending in SomeRepository from being instantiated.

7.5.2. JavaConfig

The repository infrastructure can also be triggered using a store-specific @Enable${store}Repositories annotation on a JavaConfig class. For an introduction into Java-based configuration of the Spring container, see the reference documentation.[1]

A sample configuration to enable Spring Data repositories looks something like this.

Example 20. Sample annotation based repository configuration
@Configuration
@EnableJpaRepositories("com.acme.repositories")
class ApplicationConfiguration {

  @Bean
  public EntityManagerFactory entityManagerFactory() {
    // …
  }
}
The sample uses the JPA-specific annotation, which you would change according to the store module you actually use. The same applies to the definition of the EntityManagerFactory bean. Consult the sections covering the store-specific configuration.

7.5.3. Standalone usage

You can also use the repository infrastructure outside of a Spring container, e.g. in CDI environments. You still need some Spring libraries in your classpath, but generally you can set up repositories programmatically as well. The Spring Data modules that provide repository support ship a persistence technology-specific RepositoryFactory that you can use as follows.

Example 21. Standalone usage of repository factory
RepositoryFactorySupport factory = … // Instantiate factory here
UserRepository repository = factory.getRepository(UserRepository.class);

7.6. Custom implementations for Spring Data repositories

Often it is necessary to provide a custom implementation for a few repository methods. Spring Data repositories easily allow you to provide custom repository code and integrate it with generic CRUD abstraction and query method functionality.

7.6.1. Adding custom behavior to single repositories

To enrich a repository with custom functionality you first define an interface and an implementation for the custom functionality. Use the repository interface you provided to extend the custom interface.

Example 22. Interface for custom repository functionality
interface UserRepositoryCustom {
  public void someCustomMethod(User user);
}
Example 23. Implementation of custom repository functionality
class UserRepositoryImpl implements UserRepositoryCustom {

  public void someCustomMethod(User user) {
    // Your custom implementation
  }
}
The most important bit for the class to be found is the Impl postfix of the name on it compared to the core repository interface (see below).

The implementation itself does not depend on Spring Data and can be a regular Spring bean. So you can use standard dependency injection behavior to inject references to other beans like a JdbcTemplate, take part in aspects, and so on.

Example 24. Changes to the your basic repository interface
interface UserRepository extends CrudRepository<User, Long>, UserRepositoryCustom {

  // Declare query methods here
}

Let your standard repository interface extend the custom one. Doing so combines the CRUD and custom functionality and makes it available to clients.

Configuration

If you use namespace configuration, the repository infrastructure tries to autodetect custom implementations by scanning for classes below the package we found a repository in. These classes need to follow the naming convention of appending the namespace element’s attribute repository-impl-postfix to the found repository interface name. This postfix defaults to Impl.

Example 25. Configuration example
<repositories base-package="com.acme.repository" />

<repositories base-package="com.acme.repository" repository-impl-postfix="FooBar" />

The first configuration example will try to look up a class com.acme.repository.UserRepositoryImpl to act as custom repository implementation, whereas the second example will try to lookup com.acme.repository.UserRepositoryFooBar.

Resolution of ambiguity

If multiple implementations with matching class names get found in different packages, Spring Data uses the bean names to identify the correct one to use.

Given the following two custom implementations for the UserRepository introduced above the first implementation will get picked. Its bean name is userRepositoryImpl matches that of the repository interface (userRepository) plus the postfix Impl.

Example 26. Resolution of amibiguous implementations
package com.acme.impl.one;

class UserRepositoryImpl implements UserRepositoryCustom {

  // Your custom implementation
}
package com.acme.impl.two;

@Component("specialCustomImpl")
class UserRepositoryImpl implements UserRepositoryCustom {

  // Your custom implementation
}

If you annotate the UserRepository interface with @Component("specialCustom") the bean name plus Impl matches the one defined for the repository implementation in com.acme.impl.two and it will be picked instead of the first one.

Manual wiring

The approach just shown works well if your custom implementation uses annotation-based configuration and autowiring only, as it will be treated as any other Spring bean. If your custom implementation bean needs special wiring, you simply declare the bean and name it after the conventions just described. The infrastructure will then refer to the manually defined bean definition by name instead of creating one itself.

Example 27. Manual wiring of custom implementations
<repositories base-package="com.acme.repository" />

<beans:bean id="userRepositoryImpl" class="…">
  <!-- further configuration -->
</beans:bean>

7.6.2. Adding custom behavior to all repositories

The preceding approach is not feasible when you want to add a single method to all your repository interfaces. To add custom behavior to all repositories, you first add an intermediate interface to declare the shared behavior.

Example 28. An interface declaring custom shared behavior
@NoRepositoryBean
public interface MyRepository<T, ID extends Serializable>
  extends PagingAndSortingRepository<T, ID> {

  void sharedCustomMethod(ID id);
}

Now your individual repository interfaces will extend this intermediate interface instead of the Repository interface to include the functionality declared. Next, create an implementation of the intermediate interface that extends the persistence technology-specific repository base class. This class will then act as a custom base class for the repository proxies.

Example 29. Custom repository base class
public class MyRepositoryImpl<T, ID extends Serializable>
  extends SimpleJpaRepository<T, ID> implements MyRepository<T, ID> {

  private final EntityManager entityManager;

  public MyRepositoryImpl(JpaEntityInformation entityInformation,
                          EntityManager entityManager) {
    super(entityInformation, entityManager);

    // Keep the EntityManager around to used from the newly introduced methods.
    this.entityManager = entityManager;
  }

  public void sharedCustomMethod(ID id) {
    // implementation goes here
  }
}
The class needs to have a constructor of the super class which the store-specific repository factory implementation is using. In case the repository base class has multiple constructors, override the one taking an EntityInformation plus a store specific infrastructure object (e.g. an EntityManager or a template class).

The default behavior of the Spring <repositories /> namespace is to provide an implementation for all interfaces that fall under the base-package. This means that if left in its current state, an implementation instance of MyRepository will be created by Spring. This is of course not desired as it is just supposed to act as an intermediary between Repository and the actual repository interfaces you want to define for each entity. To exclude an interface that extends Repository from being instantiated as a repository instance, you can either annotate it with @NoRepositoryBean (as seen above) or move it outside of the configured base-package.

The final step is to make the Spring Data infrastructure aware of the customized repository base class. In JavaConfig this is achieved by using the repositoryBaseClass attribute of the @Enable…Repositories annotation:

Example 30. Configuring a custom repository base class using JavaConfig
@Configuration
@EnableJpaRepositories(repositoryBaseClass = MyRepositoryImpl.class)
class ApplicationConfiguration { … }

A corresponding attribute is available in the XML namespace.

Example 31. Configuring a custom repository base class using XML
<repositories base-package="com.acme.repository"
     base-class="….MyRepositoryImpl" />

7.7. Publishing events from aggregate roots

Entities managed by repositories are aggregate roots. In a Domain-Driven Design application, these aggregate roots usually publish domain events. Spring Data provides an annotation @DomainEvents you can use on a method of your aggregate root to make that publication as easy as possible.

Example 32. Exposing domain events from an aggregate root
class AnAggregateRoot {

    @DomainEvents (1)
    Collection<Object> domainEvents() {
        // … return events you want to get published here
    }

    @AfterDomainEventsPublication (2)
    void callbackMethod() {
       // … potentially clean up domain events list
    }
}
1 The method using @DomainEvents can either return a single event instance or a collection of events. It must not take any arguments.
2 After all events have been published, a method annotated with @AfterDomainEventsPublication. It e.g. can be used to potentially clean the list of events to be published.

The methods will be called every time one of a Spring Data repository’s save(…) methods is called.

7.8. Spring Data extensions

This section documents a set of Spring Data extensions that enable Spring Data usage in a variety of contexts. Currently most of the integration is targeted towards Spring MVC.

7.8.1. Querydsl Extension

Querydsl is a framework which enables the construction of statically typed SQL-like queries via its fluent API.

Several Spring Data modules offer integration with Querydsl via QueryDslPredicateExecutor.

Example 33. QueryDslPredicateExecutor interface
public interface QueryDslPredicateExecutor<T> {

    T findOne(Predicate predicate);             (1)

    Iterable<T> findAll(Predicate predicate);   (2)

    long count(Predicate predicate);            (3)

    boolean exists(Predicate predicate);        (4)

    // … more functionality omitted.
}
1 Finds and returns a single entity matching the Predicate.
2 Finds and returns all entities matching the Predicate.
3 Returns the number of entities matching the Predicate.
4 Returns if an entity that matches the Predicate exists.

To make use of Querydsl support simply extend QueryDslPredicateExecutor on your repository interface.

Example 34. Querydsl integration on repositories
interface UserRepository extends CrudRepository<User, Long>, QueryDslPredicateExecutor<User> {

}

The above enables to write typesafe queries using Querydsl Predicate s.

Predicate predicate = user.firstname.equalsIgnoreCase("dave")
	.and(user.lastname.startsWithIgnoreCase("mathews"));

userRepository.findAll(predicate);

7.8.2. Web support

This section contains the documentation for the Spring Data web support as it is implemented as of Spring Data Commons in the 1.6 range. As it the newly introduced support changes quite a lot of things we kept the documentation of the former behavior in Legacy web support.

Spring Data modules ships with a variety of web support if the module supports the repository programming model. The web related stuff requires Spring MVC JARs on the classpath, some of them even provide integration with Spring HATEOAS [2]. In general, the integration support is enabled by using the @EnableSpringDataWebSupport annotation in your JavaConfig configuration class.

Example 35. Enabling Spring Data web support
@Configuration
@EnableWebMvc
@EnableSpringDataWebSupport
class WebConfiguration { }

The @EnableSpringDataWebSupport annotation registers a few components we will discuss in a bit. It will also detect Spring HATEOAS on the classpath and register integration components for it as well if present.

Alternatively, if you are using XML configuration, register either SpringDataWebSupport or HateoasAwareSpringDataWebSupport as Spring beans:

Example 36. Enabling Spring Data web support in XML
<bean class="org.springframework.data.web.config.SpringDataWebConfiguration" />

<!-- If you're using Spring HATEOAS as well register this one *instead* of the former -->
<bean class="org.springframework.data.web.config.HateoasAwareSpringDataWebConfiguration" />
Basic web support

The configuration setup shown above will register a few basic components:

  • A DomainClassConverter to enable Spring MVC to resolve instances of repository managed domain classes from request parameters or path variables.

  • HandlerMethodArgumentResolver implementations to let Spring MVC resolve Pageable and Sort instances from request parameters.

DomainClassConverter

The DomainClassConverter allows you to use domain types in your Spring MVC controller method signatures directly, so that you don’t have to manually lookup the instances via the repository:

Example 37. A Spring MVC controller using domain types in method signatures
@Controller
@RequestMapping("/users")
public class UserController {

  @RequestMapping("/{id}")
  public String showUserForm(@PathVariable("id") User user, Model model) {

    model.addAttribute("user", user);
    return "userForm";
  }
}

As you can see the method receives a User instance directly and no further lookup is necessary. The instance can be resolved by letting Spring MVC convert the path variable into the id type of the domain class first and eventually access the instance through calling findOne(…) on the repository instance registered for the domain type.

Currently the repository has to implement CrudRepository to be eligible to be discovered for conversion.
HandlerMethodArgumentResolvers for Pageable and Sort

The configuration snippet above also registers a PageableHandlerMethodArgumentResolver as well as an instance of SortHandlerMethodArgumentResolver. The registration enables Pageable and Sort being valid controller method arguments

Example 38. Using Pageable as controller method argument
@Controller
@RequestMapping("/users")
public class UserController {

  @Autowired UserRepository repository;

  @RequestMapping
  public String showUsers(Model model, Pageable pageable) {

    model.addAttribute("users", repository.findAll(pageable));
    return "users";
  }
}

This method signature will cause Spring MVC try to derive a Pageable instance from the request parameters using the following default configuration:

Table 1. Request parameters evaluated for Pageable instances

page

Page you want to retrieve, 0 indexed and defaults to 0.

size

Size of the page you want to retrieve, defaults to 20.

sort

Properties that should be sorted by in the format property,property(,ASC|DESC). Default sort direction is ascending. Use multiple sort parameters if you want to switch directions, e.g. ?sort=firstname&sort=lastname,asc.

To customize this behavior register a bean implementing the interface PageableHandlerMethodArgumentResolverCustomizer or SortHandlerMethodArgumentResolverCustomizer respectively. It’s customize() method will get called allowing you to change settings. Like in the following example.

@Bean SortHandlerMethodArgumentResolverCustomizer sortCustomizer() {
    return s -> s.setPropertyDelimiter("<-->");
}

If setting the properties of an existing MethodArgumentResolver isn’t sufficient for your purpose extend either SpringDataWebConfiguration or the HATEOAS-enabled equivalent and override the pageableResolver() or sortResolver() methods and import your customized configuration file instead of using the @Enable-annotation.

In case you need multiple Pageable or Sort instances to be resolved from the request (for multiple tables, for example) you can use Spring’s @Qualifier annotation to distinguish one from another. The request parameters then have to be prefixed with ${qualifier}_. So for a method signature like this:

public String showUsers(Model model,
      @Qualifier("foo") Pageable first,
      @Qualifier("bar") Pageable second) { … }

you have to populate foo_page and bar_page etc.

The default Pageable handed into the method is equivalent to a new PageRequest(0, 20) but can be customized using the @PageableDefaults annotation on the Pageable parameter.

Hypermedia support for Pageables

Spring HATEOAS ships with a representation model class PagedResources that allows enriching the content of a Page instance with the necessary Page metadata as well as links to let the clients easily navigate the pages. The conversion of a Page to a PagedResources is done by an implementation of the Spring HATEOAS ResourceAssembler interface, the PagedResourcesAssembler.

Example 39. Using a PagedResourcesAssembler as controller method argument
@Controller
class PersonController {

  @Autowired PersonRepository repository;

  @RequestMapping(value = "/persons", method = RequestMethod.GET)
  HttpEntity<PagedResources<Person>> persons(Pageable pageable,
    PagedResourcesAssembler assembler) {

    Page<Person> persons = repository.findAll(pageable);
    return new ResponseEntity<>(assembler.toResources(persons), HttpStatus.OK);
  }
}

Enabling the configuration as shown above allows the PagedResourcesAssembler to be used as controller method argument. Calling toResources(…) on it will cause the following:

  • The content of the Page will become the content of the PagedResources instance.

  • The PagedResources will get a PageMetadata instance attached populated with information form the Page and the underlying PageRequest.

  • The PagedResources gets prev and next links attached depending on the page’s state. The links will point to the URI the method invoked is mapped to. The pagination parameters added to the method will match the setup of the PageableHandlerMethodArgumentResolver to make sure the links can be resolved later on.

Assume we have 30 Person instances in the database. You can now trigger a request GET http://localhost:8080/persons and you’ll see something similar to this:

{ "links" : [ { "rel" : "next",
                "href" : "http://localhost:8080/persons?page=1&size=20 }
  ],
  "content" : [
     … // 20 Person instances rendered here
  ],
  "pageMetadata" : {
    "size" : 20,
    "totalElements" : 30,
    "totalPages" : 2,
    "number" : 0
  }
}

You see that the assembler produced the correct URI and also picks up the default configuration present to resolve the parameters into a Pageable for an upcoming request. This means, if you change that configuration, the links will automatically adhere to the change. By default the assembler points to the controller method it was invoked in but that can be customized by handing in a custom Link to be used as base to build the pagination links to overloads of the PagedResourcesAssembler.toResource(…) method.

Querydsl web support

For those stores having QueryDSL integration it is possible to derive queries from the attributes contained in a Request query string.

This means that given the User object from previous samples a query string

?firstname=Dave&lastname=Matthews

can be resolved to

QUser.user.firstname.eq("Dave").and(QUser.user.lastname.eq("Matthews"))

using the QuerydslPredicateArgumentResolver.

The feature will be automatically enabled along @EnableSpringDataWebSupport when Querydsl is found on the classpath.

Adding a @QuerydslPredicate to the method signature will provide a ready to use Predicate which can be executed via the QueryDslPredicateExecutor.

Type information is typically resolved from the methods return type. Since those information does not necessarily match the domain type it might be a good idea to use the root attribute of QuerydslPredicate. 
@Controller
class UserController {

  @Autowired UserRepository repository;

  @RequestMapping(value = "/", method = RequestMethod.GET)
  String index(Model model, @QuerydslPredicate(root = User.class) Predicate predicate,    (1)
          Pageable pageable, @RequestParam MultiValueMap<String, String> parameters) {

    model.addAttribute("users", repository.findAll(predicate, pageable));

    return "index";
  }
}
1 Resolve query string arguments to matching Predicate for User.

The default binding is as follows:

  • Object on simple properties as eq.

  • Object on collection like properties as contains.

  • Collection on simple properties as in.

Those bindings can be customized via the bindings attribute of @QuerydslPredicate or by making use of Java 8 default methods adding the QuerydslBinderCustomizer to the repository interface.

interface UserRepository extends CrudRepository<User, String>,
                                 QueryDslPredicateExecutor<User>,                (1)
                                 QuerydslBinderCustomizer<QUser> {               (2)

  @Override
  default public void customize(QuerydslBindings bindings, QUser user) {

    bindings.bind(user.username).first((path, value) -> path.contains(value))    (3)
    bindings.bind(String.class)
      .first((StringPath path, String value) -> path.containsIgnoreCase(value)); (4)
    bindings.excluding(user.password);                                           (5)
  }
}
1 QueryDslPredicateExecutor provides access to specific finder methods for Predicate.
2 QuerydslBinderCustomizer defined on the repository interface will be automatically picked up and shortcuts @QuerydslPredicate(bindings=…​).
3 Define the binding for the username property to be a simple contains binding.
4 Define the default binding for String properties to be a case insensitive contains match.
5 Exclude the password property from Predicate resolution.

7.8.3. Repository populators

If you work with the Spring JDBC module, you probably are familiar with the support to populate a DataSource using SQL scripts. A similar abstraction is available on the repositories level, although it does not use SQL as the data definition language because it must be store-independent. Thus the populators support XML (through Spring’s OXM abstraction) and JSON (through Jackson) to define data with which to populate the repositories.

Assume you have a file data.json with the following content:

Example 40. Data defined in JSON
[ { "_class" : "com.acme.Person",
 "firstname" : "Dave",
  "lastname" : "Matthews" },
  { "_class" : "com.acme.Person",
 "firstname" : "Carter",
  "lastname" : "Beauford" } ]

You can easily populate your repositories by using the populator elements of the repository namespace provided in Spring Data Commons. To populate the preceding data to your PersonRepository , do the following:

Example 41. Declaring a Jackson repository populator
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:repository="http://www.springframework.org/schema/data/repository"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/repository
    http://www.springframework.org/schema/data/repository/spring-repository.xsd">

  <repository:jackson2-populator locations="classpath:data.json" />

</beans>

This declaration causes the data.json file to be read and deserialized via a Jackson ObjectMapper.

The type to which the JSON object will be unmarshalled to will be determined by inspecting the _class attribute of the JSON document. The infrastructure will eventually select the appropriate repository to handle the object just deserialized.

To rather use XML to define the data the repositories shall be populated with, you can use the unmarshaller-populator element. You configure it to use one of the XML marshaller options Spring OXM provides you with. See the Spring reference documentation for details.

Example 42. Declaring an unmarshalling repository populator (using JAXB)
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:repository="http://www.springframework.org/schema/data/repository"
  xmlns:oxm="http://www.springframework.org/schema/oxm"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/repository
    http://www.springframework.org/schema/data/repository/spring-repository.xsd
    http://www.springframework.org/schema/oxm
    http://www.springframework.org/schema/oxm/spring-oxm.xsd">

  <repository:unmarshaller-populator locations="classpath:data.json"
    unmarshaller-ref="unmarshaller" />

  <oxm:jaxb2-marshaller contextPath="com.acme" />

</beans>

7.8.4. Legacy web support

Domain class web binding for Spring MVC

Given you are developing a Spring MVC web application you typically have to resolve domain class ids from URLs. By default your task is to transform that request parameter or URL part into the domain class to hand it to layers below then or execute business logic on the entities directly. This would look something like this:

@Controller
@RequestMapping("/users")
public class UserController {

  private final UserRepository userRepository;

  @Autowired
  public UserController(UserRepository userRepository) {
    Assert.notNull(repository, "Repository must not be null!");
    this.userRepository = userRepository;
  }

  @RequestMapping("/{id}")
  public String showUserForm(@PathVariable("id") Long id, Model model) {

    // Do null check for id
    User user = userRepository.findOne(id);
    // Do null check for user

    model.addAttribute("user", user);
    return "user";
  }
}

First you declare a repository dependency for each controller to look up the entity managed by the controller or repository respectively. Looking up the entity is boilerplate as well, as it’s always a findOne(…) call. Fortunately Spring provides means to register custom components that allow conversion between a String value to an arbitrary type.

PropertyEditors

For Spring versions before 3.0 simple Java PropertyEditors had to be used. To integrate with that, Spring Data offers a DomainClassPropertyEditorRegistrar, which looks up all Spring Data repositories registered in the ApplicationContext and registers a custom PropertyEditor for the managed domain class.

<bean class="….web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
  <property name="webBindingInitializer">
    <bean class="….web.bind.support.ConfigurableWebBindingInitializer">
      <property name="propertyEditorRegistrars">
        <bean class="org.springframework.data.repository.support.DomainClassPropertyEditorRegistrar" />
      </property>
    </bean>
  </property>
</bean>

If you have configured Spring MVC as in the preceding example, you can configure your controller as follows, which reduces a lot of the clutter and boilerplate.

@Controller
@RequestMapping("/users")
public class UserController {

  @RequestMapping("/{id}")
  public String showUserForm(@PathVariable("id") User user, Model model) {

    model.addAttribute("user", user);
    return "userForm";
  }
}

Reference Documentation

Document Structure

This part of the reference documentation explains the core functionality offered by Spring Data for Apache Cassandra.

Cassandra support introduces the Cassandra module feature set.

Cassandra repositories introduces the repository support for Cassandra.

8. Cassandra support

The Cassandra support contains a wide range of features which are summarized below.

  • Spring configuration support using Java-based @Configuration classes or the XML namespace to create a Cassandra instance with replica sets using the driver.

  • CqlTemplate helper class that increases productivity by handling common Cassandra operations properly.

  • CassandraTemplate helper class providing object mapping between CQL Tables and POJOs.

  • Exception translation into Spring’s portable Data Access Exception Hierarchy.

  • Feature rich object mapping integrated with Spring’s Conversion Service.

  • Annotation-based mapping metadata but extensible to support other metadata formats.

  • Persistence and mapping lifecycle events.

  • Java-based Query, Criteria, and Update DSLs.

  • Automatic implementation of Repository interfaces including support for custom finder methods.

For most data oriented tasks you will use the CassandraTemplate or the Repository support, which leverage the rich mapping functionality. CqlTemplate is commonly used to increment counters or perform ad-hoc CRUD operations. CqlTemplate also provides callback methods making it easy to get a hold of low-level API objects such as com.datastax.driver.core.Session allowing you to communicate directly with Cassandra. Spring Data for Apache Cassandra uses consistent naming conventions on objects in various APIs to those found in the DataStax Java Driver so that they are familiar and so you can map your existing knowledge onto the Spring APIs.

8.1. Spring CQL and Spring Data for Apache Cassandra modules

Spring Data for Apache Cassandra comes with two modules: Spring CQL and Spring Data Cassandra.

The value-add provided by the Spring Data Cassandra abstraction is perhaps best shown by the sequence of actions outlined in the table below. The table shows what actions Spring will take care of and which actions are the responsibility of you, the application developer.

Table 2. Spring CQL - who does what?
Action Spring You

Define connection parameters.

X

Open the connection.

X

Specify the CQL statement.

X

Declare parameters and provide parameter values

X

Prepare and execute the statement.

X

Set up the loop to iterate through the results (if any).

X

Do the work for each iteration.

X

Process any exception.

X

Close the Session.

X

Spring CQL takes care of all the low-level details that can make Cassandra and CQL such a tedious API to develop with. Spring Data Cassandra adds schema generation, object mapping and Repository support.

8.1.1. Choosing an approach for Cassandra database access

You can choose among several approaches to form the basis for your Cassandra database access. Spring’s support for Apache Cassandra comes in different flavors. Once you start using one of these approaches, you can still mix and match to include a feature from a different approach.

  • CqlTemplate is the classic Spring CQL approach and the most popular. This is the "lowest level" approach and all others use a CqlTemplate under the covers.

  • CassandraTemplate wraps a CqlTemplate to provide query result to object mapping and the use of SELECT, INSERT, UPDATE and DELETE methods instead of writing CQL statements. This approach provides better documentation and ease of use.

  • Repository Abstraction allows you to create Repository declarations in your data access layer. The goal of Spring Data’s Repository abstraction is to significantly reduce the amount of boilerplate code required to implement data access layers for various persistence stores.

8.2. Getting Started

Spring Apache Cassandra support requires Apache Cassandra 2.1 or higher, Datastax Java Driver 3.0 or higher and Java SE 6 or higher. An easy way to bootstrap setting up a working environment is to create a Spring-based project in STS.

First you need to set up a running Apache Cassandra server. Refer to the Apache Cassandra Quick Start guide for an explanation on how to startup Apache Cassandra. Once installed starting Cassandra is typically a matter of executing the following command: CASSANDRA_HOME/bin/cassandra -f

To create a Spring project in STS go to File → New → Spring Template Project → Simple Spring Utility Project → press Yes when prompted. Then enter a project and a package name such as org.spring.cassandra.example.

Then add the following to pom.xml dependencies section.

<dependencies>

  <dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-cassandra</artifactId>
    <version>2.0.0.M4</version>
  </dependency>

</dependencies>

Also change the version of Spring in the pom.xml to be

<spring.framework.version>5.0.0.RC2</spring.framework.version>

If using a milestone release instead of a GA release, you will also need to add the location of the Spring Milestone repository for Maven to your pom.xml which is at the same level of your <dependencies/> element.

<repositories>
  <repository>
    <id>spring-milestone</id>
    <name>Spring Maven MILESTONE Repository</name>
    <url>http://repo.spring.io/libs-milestone</url>
  </repository>
</repositories>

The repository is also browseable here.

You can also browse the Spring repositories here.

Now we will create a simple Java application that stores and reads a domain object to/from Cassandra.

First, create a simple domain object class to persist.

package org.spring.data.cassandra.example;

import org.springframework.data.cassandra.core.mapping.PrimaryKey;
import org.springframework.data.cassandra.core.mapping.Table;

@Table
public class Person {

  @PrimaryKey
  private final String id;

  private final String name;
  private final int age;

  public Person(String id, String name, int age) {
    this.id = id;
    this.name = name;
    this.age = age;
  }

  public String getId() {
    return id;
  }

  public String getName() {
    return name;
  }

  public int getAge() {
    return age;
  }

  @Override
  public String toString() {
    return String.format("{ @type = %1$s, id = %2$s, name = %3$s, age = %4$d }",
      getClass().getName(), getId(), getName(), getAge());
  }
}

Next, create the main application to run.

package org.spring.data.cassandra.example;

import java.util.UUID;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.data.cassandra.core.CassandraOperations;
import org.springframework.data.cassandra.core.CassandraTemplate;
import org.springframework.data.cassandra.core.query.Criteria;
import org.springframework.data.cassandra.core.query.Query;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.Session;

public class CassandraApplication {

  private static final Logger LOGGER = LoggerFactory.getLogger(CassandraApplication.class);

  protected static Person newPerson(String name, int age) {
    return newPerson(UUID.randomUUID().toString(), name, age);
  }

  protected static Person newPerson(String id, String name, int age) {
    return new Person(id, name, age);
  }

  public static void main(String[] args) {

    Cluster cluster = Cluster.builder().addContactPoints("localhost").build();
    Session session = cluster.connect("mykeyspace");

    CassandraOperations template = new CassandraTemplate(session);

    Person jonDoe = template.insert(newPerson("Jon Doe", 40));

    LOGGER.info(template.selectOne(Query.query(Criteria.where("id").is(jonDoe.getId())), Person.class).getId());

    template.truncate(Person.class);
    session.close();
    cluster.close();
  }
}

Even in this simple example, there are a few things to observe.

  • You can create an instance of CassandraTemplate with a Cassandra Session, derived from a Cluster.

  • You must annotate your POJO as a Cassandra @Table and also annotate the @PrimaryKey. Optionally, you can override these mapping names to match your Cassandra database table and column names.

  • You can either use a CQL String or the DataStax QueryBuilder API to construct you queries.

8.3. Examples Repository

There is a Github repository with several examples that you can download and play around with to get a feel for how the library works.

8.4. Connecting to Cassandra with Spring

One of the first tasks when using Apache Cassandra and Spring is to create a com.datastax.driver.core.Session object using the Spring IoC container. There are two main ways to do this, either using Java-based bean metadata or XML-based bean metadata. These are discussed in the following sections.

For those not familiar with how to configure the Spring container using Java-based bean metadata instead of XML-based metadata, see the high-level introduction in the reference docs here as well as the detailed documentation here.

8.4.1. Registering a Session instance using Java based metadata

An example of using Java-based bean metadata to register an instance of a com.datastax.driver.core.Session is shown below.

Example 43. Registering a com.datastax.driver.core.Session object using Java based bean metadata
@Configuration
public class AppConfig {

  /*
   * Use the standard Cassandra driver API to create a com.datastax.driver.core.Session instance.
   */
  public @Bean Session session() {
    Cluster cluster = Cluster.builder().addContactPoints("localhost").build();
    return cluster.connect("mykeyspace");
  }
}

This approach allows you to use the standard com.datastax.driver.core.Session API that you may already be used to using.

An alternative is to register an instance of com.datastax.driver.core.Session instance with the container using Spring’s CassandraCqlSessionFactoryBean and CassandraCqlClusterFactoryBean. As compared to instantiating a com.datastax.driver.core.Session instance directly, the FactoryBean approach has the added advantage of also providing the container with an ExceptionTranslator implementation that translates Cassandra exceptions to exceptions in Spring’s portable DataAccessException hierarchy for data access classes annotated. This hierarchy and use of @Repository is described in Spring’s DAO support features.

An example of a Java-based bean metadata that supports exception translation on @Repository annotated classes is shown below:

Example 44. Registering a com.datastax.driver.core.Session object using Spring’s CassandraCqlSessionFactoryBean and enabling Spring’s exception translation support
@Configuration
public class AppConfig {

  /*
   * Factory bean that creates the com.datastax.driver.core.Session instance
   */
  @Bean
  public CassandraCqlClusterFactoryBean cluster() {

    CassandraCqlClusterFactoryBean cluster = new CassandraCqlClusterFactoryBean();
    cluster.setContactPoints("localhost");

    return cluster;
  }

   /*
    * Factory bean that creates the com.datastax.driver.core.Session instance
    */
   @Bean
   public CassandraCqlSessionFactoryBean session() {

    CassandraCqlSessionFactoryBean session = new CassandraCqlSessionFactoryBean();
    session.setCluster(cluster().getObject());
    session.setKeyspaceName("mykeyspace");

    return session;
  }
}

Using CassandraTemplate with object mapping and Repository support requires a CassandraTemplate, CassandraMappingContext, CassandraConverter and enabling Repository support.

Example 45. Registering components to configure object mapping and repository support
@Configuration
@EnableCassandraRepositories(basePackages = { "org.spring.cassandra.example.repo" })
public class CassandraConfig {

  @Bean
  public CassandraClusterFactoryBean cluster() {

    CassandraClusterFactoryBean cluster = new CassandraClusterFactoryBean();
    cluster.setContactPoints("localhost");

    return cluster;
  }

  @Bean
  public CassandraMappingContext mappingContext() {

    BasicCassandraMappingContext mappingContext =  new BasicCassandraMappingContext();
    mappingContext.setUserTypeResolver(new SimpleUserTypeResolver(cluster().getObject(), "mykeyspace"));

    return mappingContext;
  }

  @Bean
  public CassandraConverter converter() {
    return new MappingCassandraConverter(mappingContext());
  }

  @Bean
  public CassandraSessionFactoryBean session() throws Exception {

    CassandraSessionFactoryBean session = new CassandraSessionFactoryBean();
    session.setCluster(cluster().getObject());
    session.setKeyspaceName("mykeyspace");
    session.setConverter(converter());
    session.setSchemaAction(SchemaAction.NONE);

    return session;
  }

  @Bean
  public CassandraOperations cassandraTemplate() throws Exception {
    return new CassandraTemplate(session().getObject());
  }
}

Creating configuration classes registering Spring Data for Apache Cassandra components can be an exhausting challenge so Spring Data for Apache Cassandra comes with a prebuilt configuration support class. Classes extending from AbstractCassandraConfiguration will register beans for Spring Data for Apache Cassandra use. AbstractCassandraConfiguration lets you provide various configuration options such as initial entities, default query options, pooling options, socket options and much more. AbstractCassandraConfiguration will support you also with schema generation based on initial entities, if any are provided. Extending from AbstractCassandraConfiguration requires you to at least provide the Keyspace name by implementing the getKeyspaceName method.

Example 46. Registering Spring Data for Apache Cassandra beans using AbstractCassandraConfiguration
@Configuration
public class AppConfig extends AbstractCassandraConfiguration {

  /*
   * Provide a contact point to the configuration.
   */
  public String getContactPoints() {
    return "localhost";
  }

  /*
   * Provide a keyspace name to the configuration.
   */
  public getKeyspaceName() {
    return "mykeyspace";
  }
}

8.4.2. XML Configuration

Externalize Connection Properties

Create a properties file containing the information needed to connect to Cassandra. contactpoints and keyspace are required fields; port has been added for clarity.

We will call this properties file, cassandra.properties.

cassandra.contactpoints=10.1.55.80,10.1.55.81
cassandra.port=9042
cassandra.keyspace=showcase

We will use Spring to load these properties into the Spring context in the next two examples.

Registering a Session instance using XML based metadata

While you can use Spring’s traditional <beans/> XML namespace to register an instance of com.datastax.driver.core.Session with the container, the XML can be quite verbose as it is general purpose. XML namespaces are a better alternative to configuring commonly used objects such as the Session instance. The cql and cassandra namespaces allow you to create a Session instance.

To use the Cassandra namespace elements you will need to reference the Cassandra schema:

Example 47. XML schema to configure Cassandra using the cql namespace
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:cql="http://www.springframework.org/schema/data/cql"
  xsi:schemaLocation="
    http://www.springframework.org/schema/cql
    http://www.springframework.org/schema/cql/spring-cql.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

  <!-- Default bean name is 'cassandraCluster' -->
  <cql:cluster contact-points="localhost" port="9042">
    <cql:keyspace action="CREATE_DROP" name="mykeyspace" />
  </cql:cluster>

  <!-- Default bean name is 'cassandraSession' -->
  <cql:session keyspace-name="mykeyspace" />

</beans>
Example 48. XML schema to configure Cassandra using the cassandra namespace
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:cassandra="http://www.springframework.org/schema/data/cassandra"
  xsi:schemaLocation="
    http://www.springframework.org/schema/data/cassandra
    http://www.springframework.org/schema/data/cassandra/spring-cassandra.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

  <!-- Default bean name is 'cassandraCluster' -->
  <cassandra:cluster contact-points="localhost" port="9042">
    <cassandra:keyspace action="CREATE_DROP" name="mykeyspace" />
  </cassandra:cluster>

  <!-- Default bean name is 'cassandraSession' -->
  <cassandra:session keyspace-name="${cassandra.keyspace}" schema-action="NONE" />

</beans>
You may have noticed the slight difference between namespaces: cql and cassandra. Using the cql namespace is limited to low-level CQL support while cassandra extends the cql namespace with object mapping and schema generation support.

The XML configuration elements for more advanced Cassandra configuration are shown below. These elements all use default bean names to keep the configuration code clean and readable.

While this example shows how easy it is to configure Spring to connect to Cassandra, there are many other options. Basically, any option available with the DataStax Java Driver is also available in the Spring Data for Apache Cassandra configuration. This is including, but not limited to Authentication, Load Balancing Policies, Retry Policies and Pooling Options. All of the Spring Data for Apache Cassandra method names and XML elements are named exactly (or as close as possible) like the configuration options on the driver so mapping any existing driver configuration should be straight forward.

Example 49. Configuring Spring Data Components via XML
<!-- Loads the properties into the Spring Context and uses them to fill
in placeholders in the bean definitions -->
<context:property-placeholder location="classpath:cassandra.properties" />

<!-- REQUIRED: The Cassandra Cluster -->
<cassandra:cluster contact-points="${cassandra.contactpoints}"
port="${cassandra.port}" />

<!-- REQUIRED: The Cassandra Session, built from the Cluster, and attaching
to a keyspace -->
<cassandra:session keyspace-name="${cassandra.keyspace}" />

<!-- REQUIRED: The Default Cassandra Mapping Context used by CassandraConverter -->
<cassandra:mapping>
  <cassandra:user-type-resolver keyspace-name="${cassandra.keyspace}" />
</cassandra:mapping>

<!-- REQUIRED: The Default Cassandra Converter used by CassandraTemplate -->
<cassandra:converter />

<!-- REQUIRED: The Cassandra Template is the building block of all Spring
Data Cassandra -->
<cassandra:template id="cassandraTemplate" />

<!-- OPTIONAL: If you are using Spring Data for Apache Cassandra Repositories, add
your base packages to scan here -->
<cassandra:repositories base-package="org.spring.cassandra.example.repo" />

8.5. Schema Management

Apache Cassandra is a data store that requires a schema definition prior to any data interaction. Spring Data for Apache Cassandra can support you with this task.

8.5.1. Keyspaces and Lifecycle scripts

The very first thing to start with is a Cassandra Keyspace. A Keyspace is a logical grouping of tables that share the same replication factor and replication strategy. Keyspace management is located in the Cluster configuration, which has the notion of KeyspaceSpecification and startup/shutdown CQL script execution.

Declaring a Keyspace with a specification allows creating/dropping of the Keyspace. It will derive CQL from the specification so you’re not required to write CQL yourself.

Example 50. Specifying a Cassandra Keyspace via XML
<cql:cluster>

    <cql:keyspace action="CREATE_DROP" durable-writes="true" name="my_keyspace">

    <cql:replication class="NETWORK_TOPOLOGY_STRATEGY">
      <cql:data-center name="foo" replication-factor="1" />
      <cql:data-center name="bar" replication-factor="2" />
    </cql:replication>
  </cql:keyspace>

</cql:cluster>
Example 51. Specifying a Cassandra Keyspace via JavaConfig
@Configuration
public abstract class AbstractCassandraConfiguration extends AbstractClusterConfiguration
		implements BeanClassLoaderAware {

  @Override
  protected List<CreateKeyspaceSpecification> getKeyspaceCreations() {

    CreateKeyspaceSpecification specification = CreateKeyspaceSpecification.createKeyspace("my_keyspace")
      .with(KeyspaceOption.DURABLE_WRITES, true)
      .withNetworkReplication(DataCenterReplication.dcr("foo", 1), DataCenterReplication.dcr("bar", 2));

    return Arrays.asList(specification);
  }

  @Override
  protected List<DropKeyspaceSpecification> getKeyspaceDrops() {
    return Arrays.asList(DropKeyspaceSpecification.dropKeyspace("my_keyspace"));
  }

  // ...
}

Startup/shutdown CQL execution follows a slightly different approach that is bound to the Cluster lifecycle. You can provide arbitrary CQL that is executed on Cluster initialization and shutdown in the SYSTEM keyspace.

Example 52. Specifying Startup/Shutdown scripts via XML
<cql:cluster>
  <cql:startup-cql><![CDATA[
CREATE KEYSPACE IF NOT EXISTS my_other_keyspace WITH durable_writes = true AND replication = { 'replication_factor' : 1, 'class' : 'SimpleStrategy' };
    ]]></cql:startup-cql>
  <cql:shutdown-cql><![CDATA[
DROP KEYSPACE my_other_keyspace;
    ]]></cql:shutdown-cql>
</cql:cluster>
Example 53. Specifying a Startup/Shutdown scripts via JavaConfig
@Configuration
public class CassandraConfiguration extends AbstractCassandraConfiguration {

  @Override
  protected List<String> getStartupScripts() {

    String script = "CREATE KEYSPACE IF NOT EXISTS my_other_keyspace "
      + "WITH durable_writes = true "
      + "AND replication = { 'replication_factor' : 1, 'class' : 'SimpleStrategy' };";

    return Arrays.asList(script);
  }

  @Override
  protected List<String> getShutdownScripts() {
    return Arrays.asList("DROP KEYSPACE my_other_keyspace;");
  }

  // ...
}
KeyspaceSpecifications and lifecycle CQL scripts are available with the cql and cassandra namespaces.
Keyspace creation allows rapid bootstrapping without the need of external Keyspace management. This can be useful for certain scenarios but should be used with care. Dropping a Keyspace on application shutdown will remove the Keyspace and all data stored inside the tables.

8.5.2. Tables and User-defined types

Spring Data for Apache Cassandra’s approaches data access with mapped entity classes that fit your data model. These entity classes can be used to create Cassandra table specifications and user type definitions.

Schema creation is tied to Session initialization with SchemaAction. Following actions are supported:

  • SchemaAction.NONE: No tables/types will be created or dropped. This is the default setting.

  • SchemaAction.CREATE: Create tables and user-defined types from entities annotated with @Table and types annotated with @UserDefinedType. Existing tables/types will cause an error if the type is attempted to be created.

  • SchemaAction.CREATE_IF_NOT_EXISTS: Like SchemaAction.CREATE but with IF NOT EXISTS applied. Existing tables/types won’t cause any errors but may remain stale.

  • SchemaAction.RECREATE: Drops and recreate existing tables and types that are known to be used. Tables and types that are not configured in the application are not dropped.

  • SchemaAction.RECREATE_DROP_UNUSED: Drop all tables and types and recreate only known tables and types.

SchemaAction.RECREATE/SchemaAction.RECREATE_DROP_UNUSED will drop your tables and you will experience data loss. RECREATE_DROP_UNUSED also drops tables and types that are not know to the application.
Enabling Tables and User-Defined Types for Schema Management

Metadata based Mapping explains object mapping using conventions and annotations. Schema management is only active for entities annotated with @Table and user-defined types annotated with @UserDefinedType to prevent unwanted classes from being created as table/type. Entities are discovered by scanning the class path. Entity scanning requires one or more base packages.

Example 54. Specifying Entity Base Packages via XML
<cassandra:mapping entity-base-packages="com.foo,com.bar"/>
Example 55. Specifying Entity Base Packages via JavaConfig
@Configuration
public class CassandraConfiguration extends AbstractCassandraConfiguration {

	@Override
	public String[] getEntityBasePackages() {
		return new String[] { "com.foo", "com.bar" };
	}

	// ...
}

8.6. CqlTemplate

The CqlTemplate class is the central class in the CQL core package. It handles the creation and release of resources. It performs the basic tasks of the core CQL workflow such as statement creation and execution, leaving application code to provide CQL and extract results. The CqlTemplate class executes CQL queries and update statements, performs iteration over ResultSets and extraction of returned parameter values. It also catches CQL exceptions and translates them to the generic, more informative, exception hierarchy defined in the org.springframework.dao package.

When you use the CqlTemplate for your code, you only need to implement callback interfaces, giving them a clearly defined contract. The PreparedStatementCreator callback interface creates a prepared statement given a Connection provided by this class, providing CQL and any necessary parameters. The RowCallbackHandler interface extracts values from each row of a ResultSet.

The CqlTemplate can be used within a DAO implementation through direct instantiation with a DataSource reference, or be configured in a Spring IoC container and given to DAOs as a bean reference. CqlTemplate is a foundational building block for CassandraTemplate.

All CQL issued by this class is logged at the DEBUG level under the category corresponding to the fully qualified class name of the template instance (typically CqlTemplate, but it may be different if you are using a custom subclass of the CqlTemplate class).

CqlTemplate comes in different execution model flavors. The basic CqlTemplate uses a blocking execution model. You can use AsyncCqlTemplate for asynchronous execution and synchronization with Futures or ReactiveCqlTemplate for reactive execution.

8.6.1. Examples of CqlTemplate class usage

This section provides some examples of CqlTemplate class usage. These examples are not an exhaustive list of all of the functionality exposed by the CqlTemplate; see the attendant javadocs for that.

Querying (SELECT)

Here is a simple query for getting the number of rows in a relation:

int rowCount = cqlTemplate.queryForObject("select count(*) from t_actor", Integer.class);

A simple query using a bind variable:

int countOfActorsNamedJoe = cqlTemplate.queryForObject(
		"select count(*) from t_actor where first_name = ?", Integer.class, "Joe");

Querying for a String:

String lastName = cqlTemplate.queryForObject(
		"select last_name from t_actor where id = ?",
		String.class, 1212L);

Querying and populating a single domain object:

Actor actor = cqlTemplate.queryForObject(
		"select first_name, last_name from t_actor where id = ?",
		new RowMapper<Actor>() {
			public Actor mapRow(Row row, int rowNum) {
				Actor actor = new Actor();
				actor.setFirstName(row.getString("first_name"));
				actor.setLastName(row.getString("last_name"));
				return actor;
			},
      new Object[]{1212L},
		});

Querying and populating a number of domain objects:

List<Actor> actors = cqlTemplate.query(
		"select first_name, last_name from t_actor",
		new RowMapper<Actor>() {
			public Actor mapRow(Row row int rowNum) {
				Actor actor = new Actor();
				actor.setFirstName(row.getString("first_name"));
				actor.setLastName(row.getString("last_name"));
				return actor;
			}
		});

If the last two snippets of code actually existed in the same application, it would make sense to remove the duplication present in the two RowMapper anonymous inner classes, and extract them out into a single class (typically a static nested class) that can then be referenced by DAO methods as needed. For example, it may be better to write the last code snippet as follows:

public List<Actor> findAllActors() {
	return cqlTemplate.query("select first_name, last_name from t_actor", new ActorMapper());
}

private static final class ActorMapper implements RowMapper<Actor> {

	public Actor mapRow(Row row, int rowNum) {
		Actor actor = new Actor();
		actor.setFirstName(row.getString("first_name"));
		actor.setLastName(row.getString("last_name"));
		return actor;
	}
}
Updating (INSERT/UPDATE/DELETE) with CqlTemplate

You use the update(…) method to perform insert, update and delete operations. Parameter values are usually provided as var args or alternatively as an object array.

cqlTemplate.execute(
		"insert into t_actor (first_name, last_name) values (?, ?)",
		"Leonor", "Watling");
cqlTemplate.execute(
		"update t_actor set last_name = ? where id = ?",
		"Banjo", 5276L);
cqlTemplate.execute(
		"delete from actor where id = ?",
		Long.valueOf(actorId));
Other CqlTemplate operations

You can use the execute(..) method to execute any arbitrary CQL, and as such the method is often used for DDL statements. It is heavily overloaded with variants taking callback interfaces, binding variable arrays, and so on.

This example shows how to create and drop a table, using different API objects, all passed to the execute() methods.

cqlOperations.execute("CREATE TABLE test_table (id uuid primary key, event text)");

DropTableSpecification dropper = DropTableSpecification.dropTable("test_table");
String cql = DropTableCqlGenerator.toCql(dropper);

cqlTemplate.execute(cql);

8.7. Exception Translation

The Spring Framework provides exception translation for a wide variety of database and mapping technologies. This has traditionally been for JDBC and JPA. The Spring support for Apache Cassandra extends this feature to Apache Cassandra by providing an implementation of the org.springframework.dao.support.PersistenceExceptionTranslator interface.

The motivation behind mapping to Spring’s consistent data access exception hierarchy is that you are then able to write portable and descriptive exception handling code without resorting to coding against Cassandra Exceptions. All of Spring’s data access exceptions are inherited from the root, DataAccessException class so you can be sure that you will be able to catch all database related exception within a single try-catch block.

8.8. Introduction to CassandraTemplate

The CassandraTemplate class, located in the package org.springframework.data.cassandra, is the central class in Spring’s Cassandra support providing a rich feature set to interact with the database. The template offers convenience operations to create, update, delete and query Cassandra and provides a mapping between your domain objects and Cassandra rows.

Once configured, CassandraTemplate is Thread-safe and can be reused across multiple instances.

The mapping between Cassandra rows and domain classes is done by delegating to an implementation of the CassandraConverter interface. Spring provides a default implementation, MappingCassandraConverter, but you can also write your own converter. Please refer to the section on Cassandra conversion for more detailed information.

The CassandraTemplate class implements the interface CassandraOperations. In as much as possible, the methods on CassandraOperations are named after methods available with Cassandra to make the API familiar to existing Cassandra developers who are familiar with Cassandra. For example, you will find methods such as "select", "insert", "delete", and "update". The design goal was to make it as easy as possible to transition between the use of the base Cassandra driver and CassandraOperations. A major difference in between the two APIs is that CassandraOperations can be passed domain objects instead of CQL and query objects.

The preferred way to reference operations on a CassandraTemplate instance is via its interface, CassandraOperations.

The default converter implementation used by CassandraTemplate is MappingCassandraConverter. While the MappingCassandraConverter can make use of additional metadata to specify the mapping of objects to rows it is also capable of converting objects that contain no additional metadata by using some conventions for the mapping of fields and table names. These conventions as well as the use of mapping annotations is explained in the Mapping chapter.

Another central feature of CassandraTemplate is exception translation of exceptions thrown in the Cassandra Java driver into Spring’s portable Data Access Exception hierarchy. Refer to the section on exception translation for more information.

Now let’s look at a examples of how to work with the CassandraTemplate in the context of the Spring container.

8.8.1. Instantiating CassandraTemplate

CassandraTemplate should always be configured as a Spring Bean, although we show an example above where you can instantiate it directly. But for the purposes of this being a Spring module, lets assume we are using the Spring Container.

CassandraTemplate is an implementation of CassandraOperations. You should always assign your CassandraTemplate to its interface definition, CassandraOperations.

There are 2 easy ways to get a CassandraTemplate, depending on how you load you Spring Application Context.

Autowiring
@Autowired
private CassandraOperations cassandraOperations;

Like all Spring Autowiring, this assumes there is only one bean of type CassandraOperations in the ApplicationContext. If you have multiple CassandraTemplate beans (which will be the case if you are working with multiple keyspaces in the same project), then use the `@Qualifier`annotation to designate which bean you want to Autowire.

@Autowired
@Qualifier("myTemplateBeanId")
private CassandraOperations cassandraOperations;
Bean Lookup with ApplicationContext

You can also just lookup the CassandraTemplate bean from the ApplicationContext.

CassandraOperations cassandraOperations = applicationContext.getBean("cassandraTemplate", CassandraOperations.class);

8.9. Saving, Updating, and Removing Rows

CassandraTemplate provides a simple way for you to save, update, and delete your domain objects, and map those objects to tables managed in Cassandra.

8.9.1. Working with Primary Keys

Cassandra requires at least one partition key field for a CQL Table. A table can declare additionally one or more clustering key fields. When your CQL Table has a composite primary key, you must create a @PrimaryKeyClass to define the structure of the composite primary key. In this context, composite primary key means one or more partition columns optionally combined with one or more clustering columns.

Primary keys can make use of any singular simple Cassandra type or mapped User-Defined Type. Collection-typed primary keys are not supported.

Simple Primary Key

A simple primary key consists of one partition key field within an entity class. Since it’s one field only, we safely can assume it’s a partition key.

Example 56. CQL Table defined in Cassandra
CREATE TABLE user (
  user_id text,
  firstname text,
  lastname text,
  PRIMARY KEY (user_id))
;
Example 57. Annotated Entity
@Table(value = "login_event")
public class LoginEvent {

  @PrimaryKey("user_id")
  private String userId;

  private String firstname;
  private String lastname;

  // getters and setters omitted for brevity

}
Composite Key

Composite primary keys (or compound keys) consist of more than one primary key fields. That said, a composite primary key can consist of multiple partition keys, a partition key and a clustering key, or a multitude of primary key fields.

Composite keys can be represented in two ways with Spring Data for Apache Cassandra:

  1. Embedded in an entity.

  2. By using @PrimaryKeyClass.

The simplest form of a composite key is a key with one partition key and one clustering key.

Here is an example of a CQL Table, and the corresponding POJOs that represent the table and it’s composite key.

Example 58. CQL Table with a Composite Primary Key
CREATE TABLE login_event(
  person_id text,
  event_code int,
  event_time timestamp,
  ip_address text,
  PRIMARY KEY (person_id, event_code, event_time))
  WITH CLUSTERING ORDER BY (event_time DESC)
;
Flat Composite Primary Key

Flat composite primary keys are embedded inside the entity as flat fields. Primary key fields are annotated with @PrimaryKeyColumn along with other fields in the entity. Selection requires either a query to contain predicates for the individual fields or the use of MapId.

Example 59. Using a flat Composite Primary Key
@Table(value = "login_event")
public class LoginEvent {

  @PrimaryKeyColumn(name = "person_id", ordinal = 0, type = PrimaryKeyType.PARTITIONED)
  private String personId;

  @PrimaryKeyColumn(name = "event_code", ordinal = 1, type = PrimaryKeyType.PARTITIONED)
  private int eventCode;

  @PrimaryKeyColumn(name = "event_time", ordinal = 2, type = PrimaryKeyType.CLUSTERED, ordering = Ordering.DESCENDING)
  private Date eventTime;

  @Column("ip_address)
  private String ipAddress;

  // getters and setters omitted for brevity
}
Primary Key Class

A primary key class is a composite primary key class that is mapped to multiple fields or properties of the entity. It’s annotated with @PrimaryKeyClass and defines equals and hashCode methods. The semantics of value equality for these methods should be consistent with the database equality for the database types to which the key is mapped. Primary key classes can be used with Repositories (as the Id type) and to represent an entities' identity in a single complex object.

Example 60. Composite Primary Key Class
@PrimaryKeyClass
public class LoginEventKey implements Serializable {

  @PrimaryKeyColumn(name = "person_id", ordinal = 0, type = PrimaryKeyType.PARTITIONED)
  private String personId;

  @PrimaryKeyColumn(name = "event_code", ordinal = 1, type = PrimaryKeyType.PARTITIONED)
  private int eventCode;

  @PrimaryKeyColumn(name = "event_time", ordinal = 2, type = PrimaryKeyType.CLUSTERED, ordering = Ordering.DESCENDING)
  private Date eventTime;

  // other methods omitted for brevity
}
Example 61. Using a Composite Primary Key
@Table(value = "login_event")
public class LoginEvent {

  @PrimaryKey
  private LoginEventKey key;

  @Column("ip_address)
  private String ipAddress;

  // getters and setters omitted for brevity
}
PrimaryKeyClass must implement Serializable and should provide implementations of hashCode() and equals().

8.9.2. Type mapping

Spring Data for Apache Cassandra relies on the DataStax Java Driver’s CodecRegistry to ensure type support. As types are added or changed, the Spring Data for Apache Cassandra module will continue to function without requiring changes. See CQL data types and Data mapping and type conversion for the current type mapping matrix.

8.9.3. Methods for inserting and updating rows

There are several convenient methods on CassandraTemplate for saving and inserting your objects. To have more fine-grained control over the conversion process you can register Spring converters with the MappingCassandraConverter, for example Converter<Row, Person>.

The difference between insert and update operations is that an INSERT operation will not insert null values.

The simple case of using the insert operation is to save a POJO. In this case the table name will be determined by name (not fully qualified) of the class. The table to store the object can be overridden using mapping metadata.

When inserting or updating, if the Id property is must be set. There are no means to generate an Id by Apache Cassandra.

Here is a basic example of using the save operation and retrieving its contents.

Example 62. Inserting and retrieving objects using the CassandraTemplate
import static org.springframework.data.cassandra.core.query.Criteria.where;
import static org.springframework.data.cassandra.core.query.Query.query;
…

Person p = new Person("Bob", 33);
cassandraTemplate.insert(p);

Person qp = cassandraTemplate.selectOne(query(where("age").is(33)), Person.class);

The insert/save operations available to you are listed below.

  • T insert (T objectToSave) Insert the object in an Apache Cassandra table.

  • T insert (T objectToSave, InsertOptions options) Insert the object in an Apache Cassandra table applying InsertOptions.

A similar set of update operations is listed below

  • T update (T objectToSave) Update the object in an Apache Cassandra table.

  • T update (T objectToSave, UpdateOptions options) Update the object in an Apache Cassandra table applying UpdateOptions.

Then, there is always the old fashioned way. You can write your own CQL statements. You can configure with InsertOptions and UpdateOptions additional options such as TTL, consistency level and lightweight transactions.

String cql = "insert into person (age, name) values (39, 'Bob')";

cqlOperations.execute(cql);
Which table will my rows be inserted into?

There are two ways to manage the collection name that is used for operating on the tables. The default table name that is used is the class name changed to start with a lower-case letter. So a com.test.Person class would be stored in the "person" table. You can customize this by providing a different collection name using the @Table annotation.

Inserting, updating and deleting individual objects in a batch

The Cassandra protocol supports inserting a collection of rows in one operation using a batch. The methods in the CassandraTemplate interface that support this functionality are listed below

  • batchOps Creates a new CassandraBatchOperations to populate the batch

CassandraBatchOperations

  • insert Takes a single object, an array (var-args) or an Iterable of objects to insert.

  • update Takes a single object, an array (var-args) or an Iterable of objects to update.

  • delete Takes a single object, an array (var-args) or an Iterable of objects to delete.

  • withTimestamp Applies a TTL to the batch.

  • execute Executes the batch.

8.9.4. Updating rows in a table

For updates we can select to update a number of rows. Here is an example of an update a single account object where we are adding a one-time $50.00 bonus to the balance using the + assignment.

Example 63. Updating rows using CasandraTemplate
import static org.springframework.data.cassandra.core.query.Criteria.where;
import org.springframework.data.cassandra.core.query.Query;
import org.springframework.data.cassandra.core.query.Update;

...

boolean applied = cassandraTemplate.update(Query.query(where("id").is("foo")),
  Update.create().increment("balance", 50.00), Account.class);

In addition to the Query discussed above we provide the update definition using an Update object. The Update class has methods that match the update assignments available for Apache Cassandra.

As you can see most methods return the Update object to provide a fluent style for the API.

Methods for executing updates for rows

  • boolean update (Query query, Update update, Class<?> entityClass) Update a selection of objects in the Apache Cassandra table.

Methods for the Update class

The Update class can be used with a little 'syntax sugar' as its methods are meant to be chained together and you can kick-start the creation of a new Update instance via the static method public static Update update(String key, Object value) and using static imports.

Here is a listing of methods on the Update class

  • AddToBuilder addTo (String columnName) AddToBuilder entry-point:

  • Update prepend(Object value) Prepend a collection value to the existing collection using the + update assignment.

  • Update prependAll(Object…​ values) Prepend all collection value to the existing collection using the + update assignment.

  • Update append(Object value) Append a collection value to the existing collection using the + update assignment.

  • Update append(Object…​ values) Append all collection value to the existing collection using the + update assignment.

  • Update entry(Object key, Object value) Add a map entry using the + update assignment.

  • Update addAll(Map<? extends Object, ? extends Object> map) Add all map entries to the map using the + update assignment.

  • Update remove (String columnName, Object value) Remove the value from the collection using the - update assignment.

  • Update clear (String columnName) Clear the collection

  • Update increment (String columnName, Number delta) Update using the + update assignment

  • Update decrement (String columnName, Number delta) Update using the - update assignment

  • Update set (String columnName, Object value) Update using the = update assignment

  • SetBuilder set (String columnName) SetBuilder entry-point:

  • Update atIndex(int index).to(Object value) Set a collection at the given index to a value using the = update assignment.

  • Update atKey(String object).to(Object value) Set a map entry at the given key to a value the = update assignment.

// UPDATE … SET key = 'Spring Data';
Update.update("key", "Spring Data")

// UPDATE … SET key[5] = 'Spring Data';
Update.empty().set("key").atIndex(5).to("Spring Data");

// UPDATE … SET key = key + ['Spring', 'DATA'];
Update.empty().addTo("key").appendAll("Spring", "Data");

Update is immutable once created. Invoking methods will create new immutable (intermediate) Update objects.

8.9.5. Methods for removing rows

You can use several overloaded methods to remove an object from the database.

  • boolean delete (Query query, Class<?> entityClass) Delete the objects selected by Query.

  • T delete (T entity) Delete the given object.

  • T delete (T entity, QueryOptions queryOptions) Delete the given object applying QueryOptions.

  • boolean deleteById (Object id, Class<?> entityClass) Delete the object using the given Id.

8.10. Querying Rows

You can express your queries using the Query and Criteria classes which have method names that reflect the native Cassandra predicates operator names such as lt, lte, is, and others. The Query and Criteria classes follow a fluent API style so that you can easily chain together multiple method criteria and queries while having easy to understand the code. Static imports in Java are used to help creating Query and Criteria instances so as to improve readability.

8.10.1. Querying rows in a table

We saw how to retrieve a single object using the selectOne method on CassandraTemplate in previous sections which return a single domain object. We can also query for a collection of rows to be returned as a list of domain objects. Assuming that we have a number of Person objects with name and age stored as rows in a table and that each person has an account balance. We can now run a query using the following code.

Example 64. Querying for rows using CassandraTemplate
import static org.springframework.data.cassandra.core.query.Criteria.where;
import static org.springframework.data.cassandra.core.query.Query.query;

…

List<Person> result = cassandraTemplate.select(query(where("age").is(50))
  .and(where("balance").gt(1000.00d)).withAllowFiltering(), Person.class);

select, selectOne and stream methods take a Query object as a parameter. This object defines the criteria and options used to perform the query. The criteria is specified using a Criteria object that has a static factory method named where used to instantiate a new Criteria object. We recommend using a static import for org.springframework.data.cassandra.core.query.Criteria.where and Query.query to make the query more readable.

This query should return a list of Person objects that meet the specified criteria. The Criteria class has the following methods that correspond to the operators provided in Apache Cassandra.

Methods for the Criteria class

  • CriteriaDefinition gt (Object value) Creates a criterion using the > operator.

  • CriteriaDefinition gte (Object value) Creates a criterion using the >= operator.

  • CriteriaDefinition in (Object…​ values) Creates a criterion using the IN operator for a varargs argument.

  • CriteriaDefinition in (Collection<?> collection) Creates a criterion using the IN operator using a collection.

  • CriteriaDefinition is (Object value) Creates a criterion using field matching (column = value).

  • CriteriaDefinition lt (Object value) Creates a criterion using the < operator.

  • CriteriaDefinition lte (Object value) Creates a criterion using the ⇐ operator.

  • CriteriaDefinition like (Object value) Creates a criterion using the LIKE operator.

  • CriteriaDefinition contains (Object value) Creates a criterion using the CONTAINS operator.

  • CriteriaDefinition containsKey (Object key) Creates a criterion using the CONTAINS KEY operator.

Criteria is immutable once created.

The Query class has some additional methods used to provide options for the query.

Methods for the Query class

  • Query by (CriteriaDefinition…​ criteria) used to create a Query object.

  • Query and (CriteriaDefinition criteria) used to add additional criteria to the query.

  • Query columns (Columns columns) used to define columns to be included in the query results.

  • Query limit (long limit) used to limit the size of the returned results to the provided limit (used for paging).

  • Query pagingState (PagingState pagingState) used to associate a PagingState with the query (used for paging).

  • Query queryOptions (QueryOptions queryOptions) used to associate QueryOptions with the query.

  • Query sort (Sort sort) used to provide sort definition for the results.

  • Query withAllowFiltering () used render ALLOW FILTERING queries.

Query is immutable once created. Invoking methods will create new immutable (intermediate) Query objects.

8.10.2. Methods for querying for rows

The query methods need to specify the target type T that will be returned.

  • List<T> select (Query query, Class<T> entityClass) Query for a list of objects of type T from the table.

  • T selectOne (Query query, Class<T> entityClass) Query for a single object of type T from the table.

  • Stream<T> stream (Query query, Class<T> entityClass) Query for a stream of objects of type T from the table.

  • List<T> select (String cql, Class<T> entityClass) Ad-hoc query for a list of objects of type T from the table providing a CQL statement.

  • T selectOne (String cql, Class<T> entityClass) Ad-hoc query for a single object of type T from the table providing a CQL statement.

  • Stream<T> stream (String cql, Class<T> entityClass) Ad-hoc query for a stream of objects of type T from the table providing a CQL statement.

8.11. Overriding default mapping with custom converters

In order to have more fine grained control over the mapping process you can register Spring converters with the CassandraConverter implementations such as the MappingCassandraConverter.

The MappingCassandraConverter checks to see if there are any Spring converters that can handle a specific class before attempting to map the object itself. To 'hijack' the normal mapping strategies of the MappingCassandraConverter, perhaps for increased performance or other custom mapping needs, you first need to create an implementation of the Spring Converter interface and then register it with the MappingCassandraConverter.

For more information on the Spring type conversion service see the reference docs here.

8.11.1. Saving using a registered Spring Converter

An example implementation of the Converter that converts a Person object to a java.lang.String using Jackson 2 is shown below:

import org.springframework.core.convert.converter.Converter;

import org.springframework.util.StringUtils;
import com.fasterxml.jackson.databind.ObjectMapper;

static class PersonWriteConverter implements Converter<Person, String> {

  public String convert(Person source) {

    try {
      return new ObjectMapper().writeValueAsString(source);
    } catch (IOException e) {
      throw new IllegalStateException(e);
    }
  }
}

8.11.2. Reading using a Spring Converter

An example implementation of the Converter that converts a java.lang.String into a Person object using Jackson 2 is shown below:

import org.springframework.core.convert.converter.Converter;

import org.springframework.util.StringUtils;
import com.fasterxml.jackson.databind.ObjectMapper;

static class PersonReadConverter implements Converter<String, Person> {

  public Person convert(String source) {

   if (StringUtils.hasText(source)) {
     try {
       return new ObjectMapper().readValue(source, Person.class);
     } catch (IOException e) {
       throw new IllegalStateException(e);
     }
    }

    return null;
  }
}

8.11.3. Registering Spring Converters with the CassandraConverter

The Spring Data for Apache Cassandra Java Config provides a convenient way to register Spring Converter`s with the `MappingCassandraConverter. The configuration snippet below shows how to manually register converters as well as configuring the CustomConversions.

@Configuration
public static class Config extends AbstractCassandraConfiguration {

  @Override
  public CustomConversions customConversions() {

    List<Converter<?, ?>> converters = new ArrayList<Converter<?, ?>>();
    converters.add(new PersonReadConverter());
    converters.add(new PersonWriteConverter());

    return new CustomConversions(converters);
  }

  // other methods omitted...
}

8.11.4. Converter disambiguation

Generally, we inspect the Converter implementations for both source and target types they convert from and to. Depending on whether one of those is a type Cassandra can handle natively, Spring Data will register the Converter instance as a reading or writing one. Have a look at the following samples:

// Write converter as only the target type is one cassandra can handle natively
class MyConverter implements Converter<Person, String> { … }

// Read converter as only the source type is one cassandra can handle natively
class MyConverter implements Converter<String, Person> { … }

In case you write a Converter whose source and target type are native Cassandra types there’s no way for Spring Data to determine whether we should consider it as reading or writing Converter. Registering the Converter instance as both might lead to unwanted results.

E.g. a Converter<String, Long> is ambiguous although it probably does not make sense to try to convert all String instances into Long instances when writing. To be generally able to force the infrastructure to register a Converter for one way only we provide @ReadingConverter as well as @WritingConverter to be used as the appropriate Converter implementation.

9. Cassandra repositories

9.1. Introduction

This chapter covers the details of the Spring Data Repository support for Apache Cassandra. Cassandra’s Repository support builds on the core Repository support explained in Working with Spring Data Repositories. So make sure you understand of the basic concepts explained there before proceeding.

9.2. Usage

To access domain entities stored in Apache Cassandra, you can leverage Spring Data’s sophisticated Repository support that eases implementing DAOs quite significantly. To do so, simply create an interface for your Repository:

Example 65. Sample Person entity
@Table
public class Person {

  @Id
  private String id;
  private String firstname;
  private String lastname;

  // … getters and setters omitted
}

We have a simple domain object here. Note that the entity has a property named id of type String. The default serialization mechanism used in CassandraTemplate (which is backing the Repository support) regards properties named id as row id.

Example 66. Basic Repository interface to persist Person entities
public interface PersonRepository extends CrudRepository<Person, String> {

  // additional custom finder methods go here
}

Right now this interface simply serves typing purposes, but we will add additional methods to it later. In your Spring configuration simply add:

Example 67. General Cassandra repository Spring configuration
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:cassandra="http://www.springframework.org/schema/data/cassandra"
  xsi:schemaLocation="
    http://www.springframework.org/schema/data/cassandra
    http://www.springframework.org/schema/data/cassandra/spring-cassandra.xsd
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

    <cassandra:cluster port="9042"/>
    <cassandra:session keyspace-name="keyspaceName"/>

    <cassandra:mapping
            entity-base-packages="com.acme.*.entities">
    </cassandra:mapping>

    <cassandra:converter/>

    <cassandra:template/>

    <cassandra:repositories base-package="com.acme.*.entities"/>
</beans>

The cassandra:repositories namespace element will cause the base packages to be scanned for interfaces extending CrudRepository and create Spring beans for each one found. By default, the Repositories will be wired with a CassandraTemplate Spring bean called cassandraTemplate, so you only need to configure cassandra-template-ref explicitly if you deviate from this convention.

If you’d rather like to go with JavaConfig use the @EnableCassandraRepositories annotation. The annotation carries the same attributes as the namespace element. If no base package is configured the infrastructure will scan the package of the annotated configuration class.

Example 68. JavaConfig for repositories
@Configuration
@EnableCassandraRepositories
class ApplicationConfig extends AbstractCassandraConfiguration {

  @Override
  protected String getKeyspaceName() {
    return "keyspace";
  }

  public String[] getEntityBasePackages() {
    return new String[] { "com.oreilly.springdata.cassandra" };
  }
}

As our domain Repository extends CrudRepository it provides you with basic CRUD operations. Working with the Repository instance is just a matter of injecting the Repository as a dependency into a client.

Example 69. Paging access to Person entities
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class PersonRepositoryTests {

    @Autowired PersonRepository repository;

    @Test
    public void readsPersonTableCorrectly() {

      List<Person> persons = repository.findAll();
      assertThat(persons.isEmpty()).isFalse();
    }
}

The sample creates an application context with Spring’s unit test support, which will perform annotation-based dependency injection into the test class. Inside the test cases (test methods) we simply use the Repository to query the data store. We invoke the Repository query method that requests the all Person instances.

9.3. Query methods

Most of the data access operations you usually trigger on a Repository result in a query being executed against the Apache Cassandra database. Defining such a query is just a matter of declaring a method on the Repository interface.

Example 70. PersonRepository with query methods
public interface PersonRepository extends CrudRepository<Person, String> {

    List<Person> findByLastname(String lastname);                      (1)

    List<Person> findByFirstname(String firstname, Sort sort);         (2)

    Person findByShippingAddress(Address address);                     (3)

    Stream<Person> findAllBy();                                        (4)
}
1 The method shows a query for all people with the given lastname. The query will be derived from parsing the method name for constraints which can be concatenated with And. Thus the method name will result in a query expression of SELECT * from person WHERE lastname = 'lastname'.
2 Applies dynamic sorting to a query. Just add a Sort parameter to your method signature and Spring Data will automatically apply ordering to the query accordingly.
3 Shows that you can query based on properties which are not a primitive type using registered Converter’s in `CustomConversions.
4 Uses a Java 8 Stream which reads and converts individual elements while iterating the stream.
Querying non-primary key properties requires secondary indexes.
Table 3. Supported keywords for query methods
Keyword Sample Logical result

After

findByBirthdateAfter(Date date)

birthdate > date

GreaterThan

findByAgeGreaterThan(int age)

age > age

GreaterThanEqual

findByAgeGreaterThanEqual(int age)

age >= age

Before

findByBirthdateBefore(Date date)

birthdate < date

LessThan

findByAgeLessThan(int age)

age < age

LessThanEqual

findByAgeLessThanEqual(int age)

age ⇐ age

In

findByAgeIn(Collection ages)

age IN (ages…​)

Like, StartingWith, EndingWith

findByFirstnameLike(String name)

firstname LIKE (name as like expression)

Containing on String

findByFirstnameContaining(String name)

firstname LIKE (name as like expression)

Containing on Collection

findByAddressesContaining(Address address)

addresses CONTAINING address

(No keyword)

findByFirstname(String name)

firstname = name

IsTrue, True

findByActiveIsTrue()

active = true

IsFalse, False

findByActiveIsFalse()

active = false

9.3.1. Projections

Spring Data Repositories usually return the domain model when using query methods. However, sometimes, you may need to alter the view of that model for various reasons. In this section, you will learn how to define projections to serve up simplified and reduced views of resources.

Look at the following domain model:

@Entity
public class Person {

  @Id @GeneratedValue
  private Long id;
  private String firstName, lastName;

  @OneToOne
  private Address address;
  …
}

@Entity
public class Address {

  @Id @GeneratedValue
  private Long id;
  private String street, state, country;

  …
}

This Person has several attributes:

  • id is the primary key

  • firstName and lastName are data attributes

  • address is a link to another domain object

Now assume we create a corresponding repository as follows:

interface PersonRepository extends CrudRepository<Person, Long> {

  Person findPersonByFirstName(String firstName);
}

Spring Data will return the domain object including all of its attributes. There are two options just to retrieve the address attribute. One option is to define a repository for Address objects like this:

interface AddressRepository extends CrudRepository<Address, Long> {}

In this situation, using PersonRepository will still return the whole Person object. Using AddressRepository will return just the Address.

However, what if you do not want to expose address details at all? You can offer the consumer of your repository service an alternative by defining one or more projections.

Example 71. Simple Projection
interface NoAddresses {  (1)

  String getFirstName(); (2)

  String getLastName();  (3)
}

This projection has the following details:

1 A plain Java interface making it declarative.
2 Export the firstName.
3 Export the lastName.

The NoAddresses projection only has getters for firstName and lastName meaning that it will not serve up any address information. The query method definition returns in this case NoAdresses instead of Person.

interface PersonRepository extends CrudRepository<Person, Long> {

  NoAddresses findByFirstName(String firstName);
}

Projections declare a contract between the underlying type and the method signatures related to the exposed properties. Hence it is required to name getter methods according to the property name of the underlying type. If the underlying property is named firstName, then the getter method must be named getFirstName otherwise Spring Data is not able to look up the source property. This type of projection is also called closed projection. Closed projections expose a subset of properties hence they can be used to optimize the query in a way to reduce the selected fields from the data store. The other type is, as you might imagine, an open projection.

Remodelling data

So far, you have seen how projections can be used to reduce the information that is presented to the user. Projections can be used to adjust the exposed data model. You can add virtual properties to your projection. Look at the following projection interface:

Example 72. Renaming a property
interface RenamedProperty {    (1)

  String getFirstName();       (2)

  @Value("#{target.lastName}")
  String getName();            (3)
}

This projection has the following details:

1 A plain Java interface making it declarative.
2 Export the firstName.
3 Export the name property. Since this property is virtual it requires @Value("#{target.lastName}") to specify the property source.

The backing domain model does not have this property so we need to tell Spring Data from where this property is obtained. Virtual properties are the place where @Value comes into play. The name getter is annotated with @Value to use SpEL expressions pointing to the backing property lastName. You may have noticed lastName is prefixed with target which is the variable name pointing to the backing object. Using @Value on methods allows defining where and how the value is obtained.

Some applications require the full name of a person. Concatenating strings with String.format("%s %s", person.getFirstName(), person.getLastName()) would be one possibility but this piece of code needs to be called in every place the full name is required. Virtual properties on projections leverage the need for repeating that code all over.

interface FullNameAndCountry {

  @Value("#{target.firstName} #{target.lastName}")
  String getFullName();

  @Value("#{target.address.country}")
  String getCountry();
}

In fact, @Value gives full access to the target object and its nested properties. SpEL expressions are extremly powerful as the definition is always applied to the projection method. Let’s take SpEL expressions in projections to the next level.

Imagine you had the following domain model definition:

@Entity
public class User {

  @Id @GeneratedValue
  private Long id;
  private String name;

  private String password;
  …
}
This example may seem a bit contrived, but it is possible with a richer domain model and many projections, to accidentally leak such details. Since Spring Data cannot discern the sensitivity of such data, it is up to the developers to avoid such situations. Storing a password as plain-text is discouraged. You really should not do this. For this example, you could also replace password with anything else that is secret.

In some cases, you might keep the password as secret as possible and not expose it more than it should be. The solution is to create a projection using @Value together with a SpEL expression.

interface PasswordProjection {
  @Value("#{(target.password == null || target.password.empty) ? null : '******'}")
  String getPassword();
}

The expression checks whether the password is null or empty and returns null in this case, otherwise six asterisks to indicate a password was set.

9.4. Miscellaneous

9.4.1. CDI Integration

Instances of the Repository interfaces are usually created by a container, and the Spring container is the most natural choice when working with Spring Data. Spring Data for Apache Cassandra ships with a custom CDI extension that allows using the repository abstraction in CDI environments. The extension is part of the JAR so all you need to do to activate it is dropping the Spring Data for Apache Cassandra JAR into your classpath. You can now set up the infrastructure by implementing a CDI Producer for the CassandraTemplate:

class CassandraTemplateProducer {

	@Produces
	@Singleton
	public Cluster createCluster() throws Exception {
		CassandraConnectionProperties properties = new CassandraConnectionProperties();

		Cluster cluster = Cluster.builder().addContactPoint(properties.getCassandraHost())
				.withPort(properties.getCassandraPort()).build();
		return cluster;
	}

	@Produces
	@Singleton
	public Session createSession(Cluster cluster) throws Exception {
		return cluster.connect();
	}

	@Produces
	@ApplicationScoped
	public CassandraOperations createCassandraOperations(Session session) throws Exception {

		MappingCassandraConverter cassandraConverter = new MappingCassandraConverter();
		cassandraConverter.setUserTypeResolver(new SimpleUserTypeResolver(session.getCluster(), session.getLoggedKeyspace()));

		CassandraAdminTemplate cassandraTemplate = new CassandraAdminTemplate(session, cassandraConverter);
		return cassandraTemplate;
	}

	public void close(@Disposes Session session) {
		session.close();
	}

	public void close(@Disposes Cluster cluster) {
		cluster.close();
	}
}

The Spring Data for Apache Cassandra CDI extension will pick up CassandraOperations available as CDI bean and create a proxy for a Spring Data Repository whenever an bean of a Repository type is requested by the container. Thus obtaining an instance of a Spring Data Repository is a matter of declaring an @Inject-ed property:

class RepositoryClient {

  @Inject
  PersonRepository repository;

  public void businessMethod() {
    List<Person> people = repository.findAll();
  }
}

10. Mapping

Rich mapping support is provided by the MappingCassandraConverter . MappingCassandraConverter has a rich metadata model that provides a complete feature set of functionality to map domain objects to CQL Tables. The mapping metadata model is populated using annotations on your domain objects. However, the infrastructure is not limited to using annotations as the only source of metadata. The MappingCassandraConverter also allows you to map domain objects to tables without providing any additional metadata, by following a set of conventions.

In this section we will describe the features of the MappingCassandraConverter, how to use conventions for mapping domain objects to tables and how to override those conventions with annotation-based mapping metadata.

10.1. Convention based Mapping

MappingCassandraConverter uses a few conventions for mapping domain objects to CQL Tables when no additional mapping metadata is provided. The conventions are:

  • The short Java class name is mapped to the table name in the following manner. The class com.bigbank.SavingsAccount maps to savingsaccount table name.

  • The converter will use any registered Spring Converters to override the default mapping of object properties to tables fields.

  • The properties of an object are used to convert to and from properties in the table.

10.2. Data mapping and type conversion

This section explains how types are mapped to an Apache Cassandra representation and vice versa.

Spring Data for Apache Cassandra supports several types that are provided by Apache Cassandra. In addition to these types, Spring Data for Apache Cassandra provides a set of built-in converters to map additional types. You can provide your own converters to adjust type conversion, see Overriding Mapping with explicit Converters for further details.

Table 4. Type
Type Cassandra types

String

text (default), varchar, ascii

double, Double

double

float, Float

float

long, Long

bigint (default), counter

int, Integer

int

short, Short

smallint

byte, Byte

tinyint

boolean, Boolean

boolean

BigInteger

varint

BigDecimal

decimal

java.util.Date

timestamp

com.datastax.driver.core.LocalDate

date

InetAddress

inet

ByteBuffer

blob

java.util.UUID

timeuuid

UDTValue, mapped User-Defined types

user type

java.util.Map<K, V>

map

java.util.List<E>

list

java.util.Set<E>

set

Enum

text (default), bigint, varint, int, smallint, tinyint

LocalDate
(Joda, Java 8, JSR310-BackPort)

date

LocalDateTime, LocalTime, Instant
(Joda, Java 8, JSR310-BackPort)

timestamp

ZoneId (Java 8, JSR310-BackPort)

text

Each supported type maps to a default Cassandra data type. Java types can be mapped to other Cassandra types by using @CassandraType.

.Enum Mapping to Numeric types
@Table
public class EnumToOrdinalMapping {

  @PrimaryKey String id;

  @CassandraType(type = Name.INT) Condition asOrdinal;
}

public enum Condition {
  NEW, USED
}
Enum mapping using ordinal values requires at least Spring 4.3.0. Using earlier Spring versions require custom converters for each Enum type.

10.2.1. Mapping Configuration

Unless explicitly configured, an instance of MappingCassandraConverter is created by default when creating a CassandraTemplate. You can create your own instance of the MappingCassandraConverter so as to tell it where to scan the classpath at startup for your domain classes in order to extract metadata and construct indexes.

Also, by creating your own instance you can register Spring Converters to use for mapping specific classes to and from the database.

Example 73. @Configuration class to configure Cassandra mapping support
@Configuration
public static class Config extends AbstractCassandraConfiguration {

  @Override
  protected String getKeyspaceName() {
    return "bigbank";
  }

  // the following are optional

  @Override
  public CustomConversions customConversions() {

    List<Converter<?, ?>> converters = new ArrayList<Converter<?, ?>>();
    converters.add(new PersonReadConverter());
    converters.add(new PersonWriteConverter());

    return new CustomConversions(converters);
  }

  @Override
  public SchemaAction getSchemaAction() {
    return SchemaAction.RECREATE;
  }

  // other methods omitted...
}

AbstractCassandraConfiguration requires you to implement methods that define a keyspace. AbstractCassandraConfiguration also has a method you can override named getEntityBasePackages(…) which tells the Converter where to scan for classes annotated with the @Table annotation.

You can add additional converters to the Converter by overriding the method customConversions.

AbstractCassandraConfiguration will create a CassandraTemplate instance and register it with the container under the name cassandraTemplate.

10.3. Metadata based Mapping

To take full advantage of the object mapping functionality inside the Spring Data for Apache Cassandra support, you should annotate your mapped objects with the @Table annotation. It allows the classpath scanner to find and pre-process your domain objects to extract the necessary metadata. Only annotated entities will be used to perform schema actions. In the worst case, a SchemaAction.RECREATE_DROP_UNUSED will drop your tables and you will experience data loss.

Example 74. Example domain object
package com.mycompany.domain;

@Table
public class Person {

  @Id
  private String id;

  @CassandraType(type = Name.VARINT)
  private Integer ssn;

  private String firstName;

  private String lastName;
}
The @Id annotation tells the mapper which property you want to use for the Cassandra primary key. Composite primary keys can require a slightly different data model.

10.3.1. Mapping annotation overview

The MappingCassandraConverter can use metadata to drive the mapping of objects to rows. An overview of the annotations is provided below:

  • @Id - applied at the field or property level to mark the property used for identity purpose.

  • @Table - applied at the class level to indicate this class is a candidate for mapping to the database. You can specify the name of the table where the object will be stored.

  • @PrimaryKey - Similar to @Id but allows you to specify the column name.

  • @PrimaryKeyColumn - Cassandra-specific annotation for primary key columns that allows you to specify primary key column attributes such as for clustered/partitioned. Can be used on single and multiple attributes to indicate either a single or a compound primary key.

  • @PrimaryKeyClass - applied at the class level to indicate this class is a compound primary key class. Requires to be referenced with @PrimaryKey.

  • @Transient - by default all private fields are mapped to the row, this annotation excludes the field where it is applied from being stored in the database.

  • @Column - applied at the field level. Describes the column name as it will be represented in the Cassandra table thus allowing the name to be different than the field name of the class.

  • @CassandraType - applied at the field level to specify a Cassandra data type. Types are derived from the declaration by default.

  • @UserDefinedType - applied at the type level to specify a Cassandra user-defined data type (UDT). Types are derived from the declaration by default.

The mapping metadata infrastructure is defined in the separate, spring-data-commons project that is technology agnostic.

Here is an example of a more complex mapping.

Example 75. Mapped Person class
@Table("my_person")
public class Person {

  @PrimaryKeyClass
  public static class Key implements Serializable {

    @PrimaryKeyColumn(ordinal = 0, type = PrimaryKeyType.PARTITIONED)
    private String type;

    @PrimaryKeyColumn(ordinal = 1, type = PrimaryKeyType.PARTITIONED)
    private String value;

    @PrimaryKeyColumn(name = "correlated_type", ordinal = 2, type = PrimaryKeyType.CLUSTERED)
    private String correlatedType;

    // other getters/setters ommitted
  }

  @PrimaryKey
  private Person.Key key;

  @CassandraType(type = Name.VARINT)
  private Integer ssn;

  @Column("f_name")
  private String firstName;

  @Column(forceQuote = true)
  private String lastName;

  private Address address;

  @CassandraType(type = Name.UDT, userTypeName = "myusertype")
  private UDTValue usertype;

  @Transient
  private Integer accountTotal;

  @CassandraType(type = Name.SET, typeArguments = Name.BIGINT)
  private Set<Long> timestamps;

  private Map<String, InetAddress> sessions;

  public Person(Integer ssn) {
    this.ssn = ssn;
  }

  public String getId() {
    return id;
  }

  // no setter for Id.  (getter is only exposed for some unit testing)

  public Integer getSsn() {
    return ssn;
  }

// other getters/setters ommitted
}
Example 76. Mapped User-Defined type Address
@UserDefinedType("address")
public class Address {

  private String city;

  @CassandraType(type = Name.VARCHAR)
  private String city;

  private Set<String> zipcodes;

  @CassandraType(type = Name.SET, typeArguments = Name.BIGINT)
  private List<Long> timestamps;

// other getters/setters ommitted
}
Working with User-Defined Types requires a UserTypeResolver configured with the mapping context. See the configuration chapter for how to configure a UserTypeResolver.

10.3.2. Overriding Mapping with explicit Converters

When storing and querying your objects it is convenient to have a CassandraConverter instance handle the mapping of all Java types to Rows. However, sometimes you may want the CassandraConverter to do most of the work but still allow you to selectively handle the conversion for a particular type, or to optimize performance.

To selectively handle the conversion yourself, register one or more org.springframework.core.convert.converter.Converter instances with the CassandraConverter.

Spring 3.0 introduced a o.s.core.convert package that provides a general type conversion system. This is described in detail in the Spring reference documentation section entitled Spring Type Conversion.

Below is an example of a Spring Converter implementation that converts from a Row to a Person POJO.

@ReadingConverter
 public class PersonReadConverter implements Converter<Row, Person> {

  public Person convert(Row source) {
    Person p = new Person(row.getString("id"));
    p.setAge(source.getInt("age");
    return p;
  }
}

Appendix

Appendix A: Namespace reference

The <repositories /> element

The <repositories /> element triggers the setup of the Spring Data repository infrastructure. The most important attribute is base-package which defines the package to scan for Spring Data repository interfaces.[3]

Table 5. Attributes
Name Description

base-package

Defines the package to be used to be scanned for repository interfaces extending *Repository (actual interface is determined by specific Spring Data module) in auto detection mode. All packages below the configured package will be scanned, too. Wildcards are allowed.

repository-impl-postfix

Defines the postfix to autodetect custom repository implementations. Classes whose names end with the configured postfix will be considered as candidates. Defaults to Impl.

query-lookup-strategy

Determines the strategy to be used to create finder queries. See Query lookup strategies for details. Defaults to create-if-not-found.

named-queries-location

Defines the location to look for a Properties file containing externally defined queries.

consider-nested-repositories

Controls whether nested repository interface definitions should be considered. Defaults to false.

Appendix B: Populators namespace reference

The <populator /> element

The <populator /> element allows to populate the a data store via the Spring Data repository infrastructure.[4]

Table 6. Attributes
Name Description

locations

Where to find the files to read the objects from the repository shall be populated with.

Appendix C: Repository query keywords

Supported query keywords

The following table lists the keywords generally supported by the Spring Data repository query derivation mechanism. However, consult the store-specific documentation for the exact list of supported keywords, because some listed here might not be supported in a particular store.

Table 7. Query keywords
Logical keyword Keyword expressions

AND

And

OR

Or

AFTER

After, IsAfter

BEFORE

Before, IsBefore

CONTAINING

Containing, IsContaining, Contains

BETWEEN

Between, IsBetween

ENDING_WITH

EndingWith, IsEndingWith, EndsWith

EXISTS

Exists

FALSE

False, IsFalse

GREATER_THAN

GreaterThan, IsGreaterThan

GREATER_THAN_EQUALS

GreaterThanEqual, IsGreaterThanEqual

IN

In, IsIn

IS

Is, Equals, (or no keyword)

IS_EMPTY

IsEmpty, Empty

IS_NOT_EMPTY

IsNotEmpty, NotEmpty

IS_NOT_NULL

NotNull, IsNotNull

IS_NULL

Null, IsNull

LESS_THAN

LessThan, IsLessThan

LESS_THAN_EQUAL

LessThanEqual, IsLessThanEqual

LIKE

Like, IsLike

NEAR

Near, IsNear

NOT

Not, IsNot

NOT_IN

NotIn, IsNotIn

NOT_LIKE

NotLike, IsNotLike

REGEX

Regex, MatchesRegex, Matches

STARTING_WITH

StartingWith, IsStartingWith, StartsWith

TRUE

True, IsTrue

WITHIN

Within, IsWithin

Appendix D: Repository query return types

Supported query return types

The following table lists the return types generally supported by Spring Data repositories. However, consult the store-specific documentation for the exact list of supported return types, because some listed here might not be supported in a particular store.

Geospatial types like (GeoResult, GeoResults, GeoPage) are only available for data stores that support geospatial queries.
Table 8. Query return types
Return type Description

void

Denotes no return value.

Primitives

Java primitives.

Wrapper types

Java wrapper types.

T

An unique entity. Expects the query method to return one result at most. In case no result is found null is returned. More than one result will trigger an IncorrectResultSizeDataAccessException.

Iterator<T>

An Iterator.

Collection<T>

A Collection.

List<T>

A List.

Optional<T>

A Java 8 or Guava Optional. Expects the query method to return one result at most. In case no result is found Optional.empty()/Optional.absent() is returned. More than one result will trigger an IncorrectResultSizeDataAccessException.

Option<T>

An either Scala or JavaSlang Option type. Semantically same behavior as Java 8’s Optional described above.

Stream<T>

A Java 8 Stream.

Future<T>

A Future. Expects method to be annotated with @Async and requires Spring’s asynchronous method execution capability enabled.

CompletableFuture<T>

A Java 8 CompletableFuture. Expects method to be annotated with @Async and requires Spring’s asynchronous method execution capability enabled.

ListenableFuture

A org.springframework.util.concurrent.ListenableFuture. Expects method to be annotated with @Async and requires Spring’s asynchronous method execution capability enabled.

Slice

A sized chunk of data with information whether there is more data available. Requires a Pageable method parameter.

Page<T>

A Slice with additional information, e.g. the total number of results. Requires a Pageable method parameter.

GeoResult<T>

A result entry with additional information, e.g. distance to a reference location.

GeoResults<T>

A list of GeoResult<T> with additional information, e.g. average distance to a reference location.

GeoPage<T>

A Page with GeoResult<T>, e.g. average distance to a reference location.
1. JavaConfig in the Spring reference documentation
2. Spring HATEOAS - https://github.com/SpringSource/spring-hateoas
3. see XML configuration
4. see XML configuration