© 2008-2018 The original authors.
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- Preface
- 1. Project Metadata
- 2. New & Noteworthy
- 3. Dependencies
- 4. Working with Spring Data Repositories
- Reference Documentation
- Appendix
Preface
1. Project Metadata
-
Version control - http://github.com/spring-projects/spring-data-jpa
-
Bugtracker - https://jira.spring.io/browse/DATAJPA
-
Release repository - https://repo.spring.io/libs-release
-
Milestone repository - https://repo.spring.io/libs-milestone
-
Snapshot repository - https://repo.spring.io/libs-snapshot
2. New & Noteworthy
2.1. What’s New in Spring Data JPA 1.11
Spring Data JPA 1.11 added the following features:
-
Improved compatibility with Hibernate 5.2.
-
Support any-match mode for Query by Example.
-
Paged query execution optimizations.
-
Support for the
exists
projection in repository query derivation.
2.2. What’s New in Spring Data JPA 1.10
Spring Data JPA 1.10 added the following features:
-
Support for Projections in repository query methods.
-
Support for Query by Example.
-
The following annotations have been enabled to build on composed annotations:
@EntityGraph
,@Lock
,@Modifying
,@Query
,@QueryHints
, and@Procedure
. -
Support for the
Contains
keyword on collection expressions. -
AttributeConverter
implementations forZoneId
of JSR-310 and ThreeTenBP. -
Upgrade to Querydsl 4, Hibernate 5, OpenJPA 2.4, and EclipseLink 2.6.1.
3. Dependencies
Due to the 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 to rely on the Spring Data Release Train BOM that we ship with the compatible versions defined. In a Maven project, you would declare this dependency in the <dependencyManagement />
section of your POM, as follows:
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-releasetrain</artifactId>
<version>Ingalls-SR16</version>
<scope>import</scope>
<type>pom</type>
</dependency>
</dependencies>
</dependencyManagement>
The current release train version is Ingalls-SR16
. The train names ascend alphabetically and the currently available trains 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
, and so on: Milestones -
RC1
,RC2
, and so on: Release candidates -
RELEASE
: GA release -
SR1
,SR2
, and so on: Service releases
A working example of using the BOMs can be found in our Spring Data examples repository. With that in place, you can declare the Spring Data modules you would like to use without a version in the <dependencies />
block, as follows:
<dependencies>
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-jpa</artifactId>
</dependency>
<dependencies>
3.1. Dependency Management with Spring Boot
Spring Boot selects a recent version of Spring Data modules for you. If you still want to upgrade to a newer version, configure the property spring-data-releasetrain.version
to the train name and iteration you would like to use.
4. Working with Spring Data Repositories
The goal of the 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. You should adapt the XML namespace declaration and the types to be extended to the equivalents of the particular module that you use. “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, see the chapter on that module of this document. |
4.1. Core concepts
The central interface in the Spring Data repository abstraction is Repository
. 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.
CrudRepository
interfacepublic 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, such as 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 such as CrudRepository .
|
On top of the CrudRepository
, there is a PagingAndSortingRepository
abstraction that adds additional methods to ease paginated access to entities:
PagingAndSortingRepository
interfacepublic interface PagingAndSortingRepository<T, ID extends Serializable>
extends CrudRepository<T, ID> {
Iterable<T> findAll(Sort sort);
Page<T> findAll(Pageable pageable);
}
To access the second page of User
by a page size of 20, you could do something like the following:
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. The following list shows the interface definition for a derived count query:
public interface UserRepository extends CrudRepository<User, Long> {
Long countByLastname(String lastname);
}
The following list shows the interface definition for a derived delete query:
public interface UserRepository extends CrudRepository<User, Long> {
Long deleteByLastname(String lastname);
List<User> removeByLastname(String lastname);
}
4.2. Query methods
Standard CRUD functionality repositories usually have queries on the underlying datastore. With Spring Data, declaring those queries becomes a four-step process:
-
Declare an interface extending Repository or one of its subinterfaces and type it to the domain class and ID type that it should handle, as shown in the following example:
interface PersonRepository extends Repository<Person, Long> { … }
-
Declare query methods on the interface.
interface PersonRepository extends Repository<Person, Long> { List<Person> findByLastname(String lastname); }
-
Set up Spring to create proxy instances for those interfaces, either with JavaConfig or with XML configuration.
-
To use Java configuration, create a class similar to the following:
import org.springframework.data.jpa.repository.config.EnableJpaRepositories; @EnableJpaRepositories class Config {}
-
To use XML configuration, define a bean similar to the following:
<?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 use the repository abstraction for any other store, you need to change this to the appropriate namespace declaration of your store module. In other words, you should exchange
jpa
in favor of, for example,mongodb
.+ Also, note that the JavaConfig variant does not configure a package explicitly, because the package of the annotated class is used by default. To customize the package to scan, use one of the
basePackage…
attributes of the data-store-specific repository’s@Enable${store}Repositories
-annotation. -
-
Inject the repository instance and use it, as shown in the following example:
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:
4.3. Defining Repository Interfaces
First, 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
.
4.3.1. Fine-tuning Repository Definition
Typically, your repository interface extends 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, copy the methods you want to expose from CrudRepository
into your domain repository.
Doing so lets you define your own abstractions on top of the provided Spring Data Repositories functionality. |
The following example shows how to selectively expose CRUD methods (findById
and save
, in this case):
@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 the prior example, you defined a common base interface for all your domain repositories and exposed findOne(…)
as well as save(…)
.These methods are routed into the base repository implementation of the store of your choice provided by Spring Data (for example, if you use JPA, the implementation is SimpleJpaRepository
), because they match the method signatures in CrudRepository
. So the UserRepository
can now save users, find individual users by ID, and trigger a query to find Users
by email address.
The intermediate repository interface is annotated with @NoRepositoryBean . Make sure you add that annotation to all repository interfaces for which Spring Data should not create instances at runtime.
|
4.3.2. Using Repositories with Multiple Spring Data Modules
Using a unique Spring Data module in your application makes things simple, because 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 cases, a repository definition must distinguish between persistence technologies. When it detects multiple repository factories on the class path, Spring Data enters strict repository configuration mode. Strict configuration uses details on the repository or the domain class to decide about Spring Data module binding for a repository definition:
-
If the repository definition extends the module-specific repository, then it is a valid candidate for the particular Spring Data module.
-
If the domain class is annotated with the module-specific type annotation, then it is a valid candidate for the particular Spring Data module. Spring Data modules accept either third-party annotations (such as JPA’s
@Entity
) or provide their own annotations (such as@Document
for Spring Data MongoDB and Spring Data Elasticsearch).
The following example shows a repository that uses module-specific interfaces (JPA in this case):
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.
The following example shows a repository that uses 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 when using a unique Spring Data module, multiple modules cannot distinguish to which particular Spring Data these repositories should be bound.
The following example shows a repository that uses 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 @Entity
annotation, so this repository clearly belongs to Spring Data JPA. UserRepository
references User
, which is annotated with Spring Data MongoDB’s @Document
annotation.
The following bad example shows a repository that uses 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 distinguishing domain class annotations are used for strict repository configuration to identify repository candidates for a particular Spring Data module. Using multiple persistence technology-specific annotations on the same domain type is possible and enables reuse of domain types across multiple persistence technologies. However, Spring Data can then no longer determine a unique module with which to bind the repository.
The last way to distinguish repositories is by scoping repository base packages. Base packages define the starting points for scanning for repository interface definitions, which implies having 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.
The following example shows annotation-driven configuration of base packages:
@EnableJpaRepositories(basePackages = "com.acme.repositories.jpa")
@EnableMongoRepositories(basePackages = "com.acme.repositories.mongo")
interface Configuration { }
4.4. Defining Query Methods
The repository proxy has two ways to derive a store-specific query from the method name:
-
By deriving the query from the method name directly.
-
By using a manually defined query.
Available options depend on the actual store. However, there must be a strategy that decides what actual query is created. The next section describes the available options.
4.4.1. Query Lookup Strategies
The following strategies are available for the repository infrastructure to resolve the query. With XML configuration, you can configure the strategy at the namespace through the query-lookup-strategy
attribute. For Java configuration, you can use the queryLookupStrategy
attribute of the Enable${store}Repositories
annotation. 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. You can read more about query construction in “Query Creation”. -
USE_DECLARED_QUERY
tries to find a declared query and throws an exception if cannot 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) combinesCREATE
andUSE_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, is 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.
4.4.2. 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
. The following example shows how to create a number of queries:
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
andOR
. You also get support for operators such asBetween
,LessThan
,GreaterThan
, andLike
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 supports ignoring case (usuallyString
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
orDesc
). To create a query method that supports dynamic sorting, see “Special parameter handling”.
4.4.3. 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. Consider the following method signature:
List<Person> findByAddressZipCode(ZipCode zipCode);
Assume a Person
has an Address
with a ZipCode
. In that case, the method creates the property traversal x.address.zipCode
. The resolution algorithm starts by 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 continues building the tree down from there, splitting the tail up in the way just described. If the first split does not match, the algorithm moves 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, choose the wrong property, and 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 be as follows:
List<Person> findByAddress_ZipCode(ZipCode zipCode);
Because we treat the underscore character as a reserved character, we strongly advise following standard Java naming conventions (that is, not using underscores in property names but using camel case instead).
4.4.4. Special parameter handling
To handle parameters in your query, define method parameters as already seen in the preceding examples. Besides that, the infrastructure recognizes certain specific types like Pageable
and Sort
, to apply pagination and sorting to your queries dynamically. The following example demonstrates these features:
Pageable
, Slice
, and Sort
in query methodsPage<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 lets you 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), you can instead return a Slice
. A Slice
only knows about whether a next Slice
is available, which might be sufficient when walking through a larger result set.
Sorting options are handled through the Pageable
instance, too. If you only need sorting, add an org.springframework.data.domain.Sort
parameter to your method. As you can see, returning a List
is also possible. In this case, the additional metadata required to build the actual Page
instance is not created (which, in turn, means that the additional count query that would have been necessary is not issued). Rather, it restricts the query to look up only the given range of entities.
To find out how many pages you get for an entire query, you have to trigger an additional count query. By default, this query is derived from the query you actually trigger. |
4.4.5. Limiting Query Results
The results of query methods can be limited by using the first
or top
keywords, which can be used interchangeably. An optional numeric value can be appended to top
or first
to specify the maximum result size to be returned.
If the number is left out, a result size of 1 is assumed. The following example shows how to limit the query size:
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 with the Optional
keyword is supported.
If pagination or slicing is applied to a limiting query pagination (and the calculation of the number of pages available), it is applied within the limited result.
Limiting the results in combination with dynamic sorting by using a Sort parameter lets you express query methods for the 'K' smallest as well as for the 'K' biggest elements.
|
4.4.6. Streaming query results
The results of query methods can be processed incrementally by using a Java 8 Stream<T>
as return type. Instead of wrapping the query results in a Stream
data store-specific methods are used to perform the streaming, as shown in the following example:
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 by using the close() method or by using a Java 7 try-with-resources block, as shown in the following example:
|
Stream<T>
result in a try-with-resources blocktry (Stream<User> stream = repository.findAllByCustomQueryAndStream()) {
stream.forEach(…);
}
Not all Spring Data modules currently support Stream<T> as a return type.
|
4.4.7. Async query results
Repository queries can be run asynchronously by using Spring’s asynchronous method execution capability. This means the method returns immediately upon invocation while the actual query execution occurs in a task that has been submitted to a Spring TaskExecutor
. Asynchronous query execution is different from reactive query execution and should not be mixed. Refer to store-specific documentation for more details on reactive support. The following example shows a number of asynchronous queries:
@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 the return type. |
2 | Use a Java 8 java.util.concurrent.CompletableFuture as the return type. |
3 | Use a org.springframework.util.concurrent.ListenableFuture as the return type. |
4.5. Creating Repository Instances
In this section, you create instances and bean definitions for the defined repository interfaces. One way to do so is by using the Spring namespace that is shipped with each Spring Data module that supports the repository mechanism, although we generally recommend using Java configuration.
4.5.1. XML configuration
Each Spring Data module includes a repositories
element that lets you define a base package that Spring scans for you, as shown in the following example:
<?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 have bean instances created for them. To do so, use <include-filter />
and <exclude-filter />
elements inside the <repositories />
element. The semantics are exactly equivalent to the elements in Spring’s context namespace. For details, see the Spring reference documentation for these elements.
For example, to exclude certain interfaces from instantiation as repository beans, you could use the following configuration:
<repositories base-package="com.acme.repositories">
<context:exclude-filter type="regex" expression=".*SomeRepository" />
</repositories>
The preceding example excludes all interfaces ending in SomeRepository
from being instantiated.
4.5.2. JavaConfig
The repository infrastructure can also be triggered by using a store-specific @Enable${store}Repositories
annotation on a JavaConfig class. For an introduction into Java-based configuration of the Spring container, see JavaConfig in the Spring reference documentation.
A sample configuration to enable Spring Data repositories resembles the following:
@Configuration
@EnableJpaRepositories("com.acme.repositories")
class ApplicationConfiguration {
@Bean
public EntityManagerFactory entityManagerFactory() {
// …
}
}
The preceding example 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. See the sections covering the store-specific configuration.
|
4.5.3. Standalone usage
You can also use the repository infrastructure outside of a Spring container — for example, 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:
RepositoryFactorySupport factory = … // Instantiate factory here
UserRepository repository = factory.getRepository(UserRepository.class);
4.6. 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.
4.6.1. 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.
interface UserRepositoryCustom {
public void someCustomMethod(User user);
}
Then you can let your repository interface additionally extend from the fragment interface, as shown in the following example:
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. Consequently, you can use standard dependency injection behavior to inject references to other beans (such as a JdbcTemplate
), take part in aspects, and so on.
You can let your repository interface extend the fragment interface, as shown in the following example:
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
.
<repositories base-package="com.acme.repository" />
<repositories base-package="com.acme.repository" repository-impl-postfix="MyPostfix" />
The first configuration example tries 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
.
Manual Wiring
If your custom implementation uses annotation-based configuration and autowiring only, the preceding approach shown works well, because it is treated as any other Spring bean. If your custom implementation bean needs special wiring, you can declare the bean and name it according to the conventions described in the preceding section. The infrastructure then refers to the manually defined bean definition by name instead of creating one itself. The following example shows how to manually wire a custom implementation:
<repositories base-package="com.acme.repository" />
<beans:bean id="userRepositoryImpl" class="…">
<!-- further configuration -->
</beans:bean>
4.6.2. 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.
@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.
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 uses. If the repository base class has multiple constructors, override the one taking an EntityInformation plus a store specific infrastructure object (such as 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 Java configuration, you can do so by using the repositoryBaseClass
attribute of the @Enable${store}Repositories
annotation, as shown in the following example:
@Configuration
@EnableJpaRepositories(repositoryBaseClass = MyRepositoryImpl.class)
class ApplicationConfiguration { … }
A corresponding attribute is available in the XML namespace, as shown in the following example:
<repositories base-package="com.acme.repository"
base-class="….MyRepositoryImpl" />
4.7. 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 called @DomainEvents
that you can use on a method of your aggregate root to make that publication as easy as possible, as shown in the following example:
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 return either a single event instance or a collection of events. It must not take any arguments. |
2 | After all events have been published, we have a method annotated with @AfterDomainEventsPublication . It can be used to potentially clean the list of events to be published (among other uses). |
The methods are called every time one of a Spring Data repository’s save(…)
methods is called.
4.8. 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.
4.8.1. Querydsl Extension
Querydsl is a framework that enables the construction of statically typed SQL-like queries through its fluent API.
Several Spring Data modules offer integration with Querydsl through QueryDslPredicateExecutor
, as shown in the following example:
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 whether an entity that matches the Predicate exists. |
To make use of Querydsl support, extend QueryDslPredicateExecutor
on your repository interface, as shown in the following example
interface UserRepository extends CrudRepository<User, Long>, QueryDslPredicateExecutor<User> {
}
The preceding example lets you write typesafe queries using Querydsl Predicate
instances, as shown in the following example:
Predicate predicate = user.firstname.equalsIgnoreCase("dave")
.and(user.lastname.startsWithIgnoreCase("mathews"));
userRepository.findAll(predicate);
4.8.2. Web support
This section contains the documentation for the Spring Data web support as it is implemented in the current (and later) versions of Spring Data Commons. As the newly introduced support changes many things, we kept the documentation of the former behavior in Legacy web support. |
Spring Data modules that support the repository programming model ship with a variety of web support. The web related components require Spring MVC JARs to be on the classpath. Some of them even provide integration with Spring HATEOAS. In general, the integration support is enabled by using the @EnableSpringDataWebSupport
annotation in your JavaConfig configuration class, as shown in the following example:
@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 use XML configuration, register either SpringDataWebConfiguration
or HateoasAwareSpringDataWebConfiguration
as Spring beans, as shown in the following example (for SpringDataWebConfiguration
):
<bean class="org.springframework.data.web.config.SpringDataWebConfiguration" />
<!-- If you use Spring HATEOAS, register this one *instead* of the former -->
<bean class="org.springframework.data.web.config.HateoasAwareSpringDataWebConfiguration" />
Basic Web Support
The configuration shown in the previous section registers a few basic components:
-
A
DomainClassConverter
to let Spring MVC resolve instances of repository-managed domain classes from request parameters or path variables. -
HandlerMethodArgumentResolver
implementations to let Spring MVC resolvePageable
andSort
instances from request parameters.
DomainClassConverter
The DomainClassConverter
lets you use domain types in your Spring MVC controller method signatures directly, so that you need not manually lookup the instances through the repository, as shown in the following example:
@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 shown in the previous section also registers a PageableHandlerMethodArgumentResolver
as well as an instance of SortHandlerMethodArgumentResolver
. The registration enables Pageable
and Sort
as valid controller method arguments, as shown in the following example:
@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";
}
}
The preceding method signature causes Spring MVC try to derive a Pageable
instance from the request parameters by using the following default configuration:
|
Page you want to retrieve. 0-indexed and defaults to 0. |
|
Size of the page you want to retrieve. Defaults to 20. |
|
Properties that should be sorted by in the format |
To customize this behavior 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.
If 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}_
. The followig example shows the resulting method signature:
public String showUsers(Model model,
@Qualifier("thing1") Pageable first,
@Qualifier("thing2") Pageable second) { … }
you have to populate thing1_page
and thing2_page
and so on.
The default Pageable
passed into the method is equivalent to a new PageRequest(0, 20)
but can be customized by using the @PageableDefault
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, called the PagedResourcesAssembler
. The following example shows how to use a PagedResourcesAssembler
as a 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 in the preceding example lets the PagedResourcesAssembler
be used as a controller method argument. Calling toResources(…)
on it has the following effects:
-
The content of the
Page
becomes the content of thePagedResources
instance. -
The
PagedResources
object gets aPageMetadata
instance attached, and it is populated with information from thePage
and the underlyingPageRequest
. -
The
PagedResources
may getprev
andnext
links attached, depending on the page’s state. The links point to the URI to which the method maps. The pagination parameters added to the method match the setup of thePageableHandlerMethodArgumentResolver
to make sure the links can be resolved later.
Assume we have 30 Person instances in the database. You can now trigger a request (GET http://localhost:8080/persons
) and see output similar to the following:
{ "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 picked up the default configuration to resolve the parameters into a Pageable
for an upcoming request. This means that, if you change that configuration, the links 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, which overloads the PagedResourcesAssembler.toResource(…)
method.
Web Databinding Support
Spring Data projections (described in Projections) can be used to bind incoming request payloads by either using JSONPath expressions (requires Jayway JsonPath or XPath expressions (requires XmlBeam), as shown in the following example:
@ProjectedPayload
public interface UserPayload {
@XBRead("//firstname")
@JsonPath("$..firstname")
String getFirstname();
@XBRead("/lastname")
@JsonPath({ "$.lastname", "$.user.lastname" })
String getLastname();
}
The type shown in the preceding example can be used as a Spring MVC handler method argument or by using ParameterizedTypeReference
on one of RestTemplate
's methods.
The preceding method declarations would try to find firstname
anywhere in the given document.
The lastname
XML lookup is performed on the top-level of the incoming document.
The JSON variant of that tries a top-level lastname
first but also tries lastname
nested in a user
sub-document if the former does not return a value.
That way, changes in the structure of the source document can be mitigated easily without having clients calling the exposed methods (usually a drawback of class-based payload binding).
Nested projections are supported as described in Projections.
If the method returns a complex, non-interface type, a Jackson ObjectMapper
is used to map the final value.
For Spring MVC, the necessary converters are registered automatically as soon as @EnableSpringDataWebSupport
is active and the required dependencies are available on the classpath.
For usage with RestTemplate
, register a ProjectingJackson2HttpMessageConverter
(JSON) or XmlBeamHttpMessageConverter
manually.
For more information, see the web projection example in the canonical Spring Data Examples repository.
Querydsl Web Support
For those stores having QueryDSL integration, it is possible to derive queries from the attributes contained in a Request
query string.
Consider the following query string:
?firstname=Dave&lastname=Matthews
Given the User
object from previous examples, a query string can be resolved to the following value by using the QuerydslPredicateArgumentResolver
.
QUser.user.firstname.eq("Dave").and(QUser.user.lastname.eq("Matthews"))
The feature is automatically enabled, along with @EnableSpringDataWebSupport , when Querydsl is found on the classpath.
|
Adding a @QuerydslPredicate
to the method signature provides a ready-to-use Predicate
, which can be run by using the QuerydslPredicateExecutor
.
Type information is typically resolved from the method’s return type. Since that information does not necessarily match the domain type, it might be a good idea to use the root attribute of QuerydslPredicate .
|
The following exampe shows how to use @QuerydslPredicate
in a method signature:
@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 aseq
. -
Object
on collection like properties ascontains
. -
Collection
on simple properties asin
.
Those bindings can be customized through the bindings
attribute of @QuerydslPredicate
or by making use of Java 8 default methods
and adding the QuerydslBinderCustomizer
method 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 is 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. |
4.8.3. Repository Populators
If you work with the Spring JDBC module, you are probably familiar with the support to populate a DataSource
with 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:
[ { "_class" : "com.acme.Person",
"firstname" : "Dave",
"lastname" : "Matthews" },
{ "_class" : "com.acme.Person",
"firstname" : "Carter",
"lastname" : "Beauford" } ]
You can 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, declare a populator similar to the following:
<?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>
The preceding declaration causes the data.json
file to
be read and deserialized by a Jackson ObjectMapper
.
The type to which the JSON object is unmarshalled is determined by inspecting the _class
attribute of the JSON document. The infrastructure eventually selects the appropriate repository to handle the object that was deserialized.
To instead use XML to define the data the repositories should be populated with, you can use the unmarshaller-populator
element. You configure it to use one of the XML marshaller options available in Spring OXM. See the Spring reference documentation for details. The following example shows how to unmarshal a repository populator with 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>
4.8.4. 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
5. JPA Repositories
This chapter points out the specialties for repository support for JPA. This builds on the core repository support explained in “Working with Spring Data Repositories”. Make sure you have a sound understanding of the basic concepts explained there.
5.1. Introduction
This section describes the basics of configuring Spring Data JPA through either:
-
“Spring Namespace” (XML configuration)
-
“Annotation-based Configuration” (Java configuration)
5.1.1. Spring Namespace
The JPA module of Spring Data contains a custom namespace that allows defining repository beans. It also contains certain features and element attributes that are special to JPA. Generally, the JPA repositories can be set up by using the repositories
element, as shown in the following example:
<?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>
Using the repositories
element looks up Spring Data repositories as described in “Creating Repository Instances”. Beyond that, it activates persistence exception translation for all beans annotated with @Repository
, to let exceptions being thrown by the JPA persistence providers be converted into Spring’s DataAccessException
hierarchy.
Custom Namespace Attributes
Beyond the default attributes of the repositories
element, the JPA namespace offers additional attributes to let you gain more detailed control over the setup of the repositories:
|
Explicitly wire the |
|
Explicitly wire the |
Spring Data JPA requires a PlatformTransactionManager bean named transactionManager to be present if no explicit transaction-manager-ref is defined.
|
5.1.2. Annotation-based Configuration
The Spring Data JPA repositories support can be activated not only through an XML namespace but also by using an annotation through JavaConfig, as shown in the following example:
@Configuration
@EnableJpaRepositories
@EnableTransactionManagement
class ApplicationConfig {
@Bean
public DataSource dataSource() {
EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
return builder.setType(EmbeddedDatabaseType.HSQL).build();
}
@Bean
public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
vendorAdapter.setGenerateDdl(true);
LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
factory.setJpaVendorAdapter(vendorAdapter);
factory.setPackagesToScan("com.acme.domain");
factory.setDataSource(dataSource());
return factory;
}
@Bean
public PlatformTransactionManager transactionManager(EntityManagerFactory entityManagerFactory) {
JpaTransactionManager txManager = new JpaTransactionManager();
txManager.setEntityManagerFactory(entityManagerFactory);
return txManager;
}
}
You must create LocalContainerEntityManagerFactoryBean and not EntityManagerFactory directly, since the former also participates in exception translation mechanisms in addition to creating EntityManagerFactory .
|
The preceding configuration class sets up an embedded HSQL database by using the EmbeddedDatabaseBuilder
API of spring-jdbc
. Spring Data then sets up an EntityManagerFactory
and uses Hibernate as the sample persistence provider. The last infrastructure component declared here is the JpaTransactionManager
. Finally, the example activates Spring Data JPA repositories by using the @EnableJpaRepositories
annotation, which essentially carries the same attributes as the XML namespace. If no base package is configured, it uses the one in which the configuration class resides.
5.2. Persisting Entities
This section describes how to persist (save) entities with Spring Data JPA.
5.2.1. Saving Entities
Saving an entity can be performed with the CrudRepository.save(…)
method. It persists or merges the given entity by using the underlying JPA EntityManager
. If the entity has not yet been persisted, Spring Data JPA saves the entity with a call to the entityManager.persist(…)
method. Otherwise, it calls the entityManager.merge(…)
method.
Entity State-detection Strategies
Spring Data JPA offers the following strategies to detect whether an entity is new or not:
-
Id-Property inspection (default): By default Spring Data JPA inspects the identifier property of the given entity. If the identifier property is
null
, then the entity is assumed to be new. Otherwise, it is assumed to be not new. -
Implementing
Persistable
: If an entity implementsPersistable
, Spring Data JPA delegates the new detection to theisNew(…)
method of the entity. See the JavaDoc for details. -
Implementing
EntityInformation
: You can customize theEntityInformation
abstraction used in theSimpleJpaRepository
implementation by creating a subclass ofJpaRepositoryFactory
and overriding thegetEntityInformation(…)
method accordingly. You then have to register the custom implementation ofJpaRepositoryFactory
as a Spring bean. Note that this should be rarely necessary. See the JavaDoc for details.
5.3. Query Methods
This section describes the various ways to create a query with Spring Data JPA.
5.3.1. Query Lookup Strategies
The JPA module supports defining a query manually as a String or having it being derived from the method name.
Declared Queries
Although getting a query derived from the method name is quite convenient, one might face the situation in which either the method name parser does not support the keyword one wants to use or the method name would get unnecessarily ugly. So you can either use JPA named queries through a naming convention (see Using JPA Named Queries for more information) or rather annotate your query method with @Query
(see Using @Query
for details).
5.3.2. Query Creation
Generally, the query creation mechanism for JPA works as described in “Query methods”. The following example shows what a JPA query method translates into:
public interface UserRepository extends Repository<User, Long> { List<User> findByEmailAddressAndLastname(String emailAddress, String lastname); }
We create a query using the JPA criteria API from this, but, essentially, this translates into the following query: select u from User u where u.emailAddress = ?1 and u.lastname = ?2
. Spring Data JPA does a property check and traverses nested properties, as described in “Property Expressions”.
The following table describes the keywords supported for JPA and what a method containing that keyword translates to:
Keyword | Sample | JPQL snippet |
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In and NotIn also take any subclass of Collection as aparameter as well as arrays or varargs. For other syntactical versions of the same logical operator, check “Repository query keywords”.
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5.3.3. Using JPA Named Queries
The examples use the <named-query /> element and @NamedQuery annotation. The queries for these configuration elements have to be defined in the JPA query language. Of course, you can use <named-native-query /> or @NamedNativeQuery too. These elements let you define the query in native SQL by losing the database platform independence.
|
XML Named Query Definition
To use XML configuration, add the necessary <named-query />
element to the orm.xml
JPA configuration file located in the META-INF
folder of your classpath. Automatic invocation of named queries is enabled by using some defined naming convention. For more details, see below.
<named-query name="User.findByLastname">
<query>select u from User u where u.lastname = ?1</query>
</named-query>
The query has a special name that is used to resolve it at runtime.
Annotation-based Configuration
Annotation-based configuration has the advantage of not needing another configuration file to be edited, lowering maintenance effort. You pay for that benefit by the need to recompile your domain class for every new query declaration.
@Entity
@NamedQuery(name = "User.findByEmailAddress",
query = "select u from User u where u.emailAddress = ?1")
public class User {
}
Declaring Interfaces
To allow execution of these named queries, specify the UserRepository
as follows:
public interface UserRepository extends JpaRepository<User, Long> {
List<User> findByLastname(String lastname);
User findByEmailAddress(String emailAddress);
}
Spring Data tries to resolve a call to these methods to a named query, starting with the simple name of the configured domain class, followed by the method name separated by a dot. So the preceding example would use the named queries defined in the examlpe instead of trying to create a query from the method name.
5.3.4. Using @Query
Using named queries to declare queries for entities is a valid approach and works fine for a small number of queries. As the queries themselves are tied to the Java method that executes them, you can actually bind them directly by using the Spring Data JPA @Query
annotation rather than annotating them to the domain class. This frees the domain class from persistence specific information and co-locates the query to the repository interface.
Queries annotated to the query method take precedence over queries defined using @NamedQuery
or named queries declared in orm.xml
.
The following example shows a query created with the @Query
annotation:
@Query
public interface UserRepository extends JpaRepository<User, Long> {
@Query("select u from User u where u.emailAddress = ?1")
User findByEmailAddress(String emailAddress);
}
Using Advanced LIKE
Expressions
The query execution mechanism for manually defined queries created with @Query
allows the definition of advanced LIKE
expressions inside the query definition, as shown in the following example:
like
expressions in @Querypublic interface UserRepository extends JpaRepository<User, Long> {
@Query("select u from User u where u.firstname like %?1")
List<User> findByFirstnameEndsWith(String firstname);
}
In the preceding example, the LIKE
delimiter character (%
) is recognized, and the query is transformed into a valid JPQL query (removing the %
). Upon query execution, the parameter passed to the method call gets augmented with the previously recognized LIKE
pattern.
Native Queries
The @Query
annotation allows for running native queries by setting the nativeQuery
flag to true, as shown in the following example:
public interface UserRepository extends JpaRepository<User, Long> {
@Query(value = "SELECT * FROM USERS WHERE EMAIL_ADDRESS = ?1", nativeQuery = true)
User findByEmailAddress(String emailAddress);
}
Spring Data JPA does not currently support dynamic sorting for native queries, because it would have to manipulate the actual query declared, which it cannot do reliably for native SQL. You can, however, use native queries for pagination by specifying the count query yourself, as shown in the following example: |
@Query
public interface UserRepository extends JpaRepository<User, Long> {
@Query(value = "SELECT * FROM USERS WHERE LASTNAME = ?1",
countQuery = "SELECT count(*) FROM USERS WHERE LASTNAME = ?1",
nativeQuery = true)
Page<User> findByLastname(String lastname, Pageable pageable);
}
A similar approach also works with named native queries, by adding the .count
suffix to a copy of your query. You probably need to register a result set mapping for your count query, though.
5.3.5. Using Sort
Sorting can be done be either providing a PageRequest
or by using Sort
directly. The properties actually used within the Order
instances of Sort
need to match your domain model, which means they need to resolve to either a property or an alias used within the query. The JPQL defines this as a state field path expression.
Using any non-referenceable path expression leads to an Exception .
|
However, using Sort
together with @Query
lets you sneak in non-path-checked Order
instances containing functions within the ORDER BY
clause. This is possible because the Order
is appended to the given query string. By default, Spring Data JPA rejects any Order
instance containing function calls, but you can use JpaSort.unsafe
to add potentially unsafe ordering.
The following example uses Sort
and JpaSort
, including an unsafe option on JpaSort
:
Sort
and JpaSort
public interface UserRepository extends JpaRepository<User, Long> {
@Query("select u from User u where u.lastname like ?1%")
List<User> findByAndSort(String lastname, Sort sort);
@Query("select u.id, LENGTH(u.firstname) as fn_len from User u where u.lastname like ?1%")
List<Object[]> findByAsArrayAndSort(String lastname, Sort sort);
}
repo.findByAndSort("lannister", new Sort("firstname")); (1)
repo.findByAndSort("stark", new Sort("LENGTH(firstname)")); (2)
repo.findByAndSort("targaryen", JpaSort.unsafe("LENGTH(firstname)")); (3)
repo.findByAsArrayAndSort("bolton", new Sort("fn_len")); (4)
1 | Valid Sort expression pointing to property in domain model. |
2 | Invalid Sort containing function call. Thows Exception. |
3 | Valid Sort containing explicitly unsafe Order . |
4 | Valid Sort expression pointing to aliased function. |
5.3.6. Using Named Parameters
By default, Spring Data JPA uses position-based parameter binding, as described in all the preceding examples. This makes query methods a little error-prone when refactoring regarding the parameter position. To solve this issue, you can use @Param
annotation to give a method parameter a concrete name and bind the name in the query, as shown in the following example:
public interface UserRepository extends JpaRepository<User, Long> {
@Query("select u from User u where u.firstname = :firstname or u.lastname = :lastname")
User findByLastnameOrFirstname(@Param("lastname") String lastname,
@Param("firstname") String firstname);
}
The method parameters are switched according to their order in the defined query. |
As of version 4, Spring fully supports Java 8’s parameter name discovery based on the -parameters compiler flag. By using this flag in your build as an alternative to debug information, you can omit the @Param annotation for named parameters.
|
5.3.7. Using SpEL Expressions
As of Spring Data JPA release 1.4, we support the usage of restricted SpEL template expressions in manually defined queries that are defined with @Query
. Upon query execution, these expressions are evaluated against a predefined set of variables. Spring Data JPA supports a variable called entityName
. Its usage is select x from #{#entityName} x
. It inserts the entityName
of the domain type associated with the given repository. The entityName
is resolved as follows: If the domain type has set the name property on the @Entity
annotation, it is used. Otherwise, the simple class-name of the domain type is used.
The following example demonstrates one use case for the #{#entityName}
expression in a query string where you want to define a repository interface with a query method and a manually defined query:
@Entity
public class User {
@Id
@GeneratedValue
Long id;
String lastname;
}
public interface UserRepository extends JpaRepository<User,Long> {
@Query("select u from #{#entityName} u where u.lastname = ?1")
List<User> findByLastname(String lastname);
}
To avoid stating the actual entity name in the query string of a @Query
annotation, you can use the #{#entityName}
variable.
The entityName can be customized by using the @Entity annotation. Customizations in orm.xml are not supported for the SpEL expressions.
|
Of course, you could have just used User
in the query declaration directly, but that would require you to change the query as well. The reference to #entityName
picks up potential future remappings of the User
class to a different entity name (for example, by using @Entity(name = "MyUser")
.
Another use case for the #{#entityName}
expression in a query string is if you want to define a generic repository interface with specialized repository interfaces for a concrete domain type. To not repeat the definition of custom query methods on the concrete interfaces, you can use the entity name expression in the query string of the @Query
annotation in the generic repository interface, as shown in the following example:
@MappedSuperclass
public abstract class AbstractMappedType {
…
String attribute
}
@Entity
public class ConcreteType extends AbstractMappedType { … }
@NoRepositoryBean
public interface MappedTypeRepository<T extends AbstractMappedType>
extends Repository<T, Long> {
@Query("select t from #{#entityName} t where t.attribute = ?1")
List<T> findAllByAttribute(String attribute);
}
public interface ConcreteRepository
extends MappedTypeRepository<ConcreteType> { … }
In the preceding example, the MappedTypeRepository
interface is the common parent interface for a few domain types extending AbstractMappedType
. It also defines the generic findAllByAttribute(…)
method, which can be used on instances of the specialized repository interfaces. If you now invoke findByAllAttribute(…)
on ConcreteRepository
, the query becomes select t from ConcreteType t where t.attribute = ?1
.
5.3.8. Modifying Queries
All the previous sections describe how to declare queries to access a given entity or collection of entities. You can add custom modifying behavior by using the facilities described in “Custom implementations for Spring Data repositories”. As this approach is feasible for comprehensive custom functionality, you can modify queries that only need parameter binding by annotating the query method with @Modifying
, as shown in the following example:
@Modifying
@Query("update User u set u.firstname = ?1 where u.lastname = ?2")
int setFixedFirstnameFor(String firstname, String lastname);
Doing so triggers the query annotated to the method as an updating query instead of a selecting one. As the EntityManager
might contain outdated entities after the execution of the modifying query, we do not automatically clear it (see the JavaDoc of EntityManager.clear()
for details), since this effectively drops all non-flushed changes still pending in the EntityManager
. If you wish the EntityManager
to be cleared automatically, you can set the @Modifying
annotation’s clearAutomatically
attribute to true
.
Derived Delete Queries
Spring Data JPA also supports derived delete queries that let you avoid having to declare the JPQL query explicitly, as shown in the following example:
interface UserRepository extends Repository<User, Long> {
void deleteByRoleId(long roleId);
@Modifying
@Query("delete from User u where user.role.id = ?1")
void deleteInBulkByRoleId(long roleId);
}
Although the deleteByRoleId(…)
method looks like it basically produces the same result as the deleteInBulkByRoleId(…)
, there is an important difference between the two method declarations in terms of the way they get executed.
As the name suggests, the latter method issues a single JPQL query (the one defined in the annotation) against the database.
This means even currently loaded instances of User
do not see lifecycle callbacks invoked.
To make sure lifecycle queries are actually invoked, an invocation of deleteByRoleId(…)
executes a query and then deletes the returned instances one by one, so that the persistence provider can actually invoke @PreRemove
callbacks on those entities.
In fact, a derived delete query is a shortcut for executing the query and then calling CrudRepository.delete(Iterable<User> users)
on the result and keeping behavior in sync with the implementations of other delete(…)
methods in CrudRepository
.
5.3.9. Applying Query Hints
To apply JPA query hints to the queries declared in your repository interface, you can use the @QueryHints
annotation. It takes an array of JPA @QueryHint
annotations plus a boolean flag to potentially disable the hints applied to the additional count query triggered when applying pagination, as shown in the following example:
public interface UserRepository extends Repository<User, Long> {
@QueryHints(value = { @QueryHint(name = "name", value = "value")},
forCounting = false)
Page<User> findByLastname(String lastname, Pageable pageable);
}
The preceding declaration would apply the configured @QueryHint
for that actually query but omit applying it to the count query triggered to calculate the total number of pages.
5.3.10. Configuring Fetch- and LoadGraphs
The JPA 2.1 specification introduced support for specifying Fetch- and LoadGraphs that we also support with the @EntityGraph
annotation, which lets you reference a @NamedEntityGraph
definition. You can use that annotation on an entity to configure the fetch plan of the resulting query. The type (Fetch
or Load
) of the fetching can be configured by using the type
attribute on the @EntityGraph
annotation. See the JPA 2.1 Spec 3.7.4 for further reference.
The following example shows how to define a named entity graph on an entity:
@Entity
@NamedEntityGraph(name = "GroupInfo.detail",
attributeNodes = @NamedAttributeNode("members"))
public class GroupInfo {
// default fetch mode is lazy.
@ManyToMany
List<GroupMember> members = new ArrayList<GroupMember>();
…
}
The following example shows how to reference a named entity graph on a repository query method:
@Repository
public interface GroupRepository extends CrudRepository<GroupInfo, String> {
@EntityGraph(value = "GroupInfo.detail", type = EntityGraphType.LOAD)
GroupInfo getByGroupName(String name);
}
It is also possible to define ad hoc entity graphs by using @EntityGraph
. The provided attributePaths
are translated into the according EntityGraph
without needing to explicitly add @NamedEntityGraph
to your domain types, as shown in the following example:
@Repository
public interface GroupRepository extends CrudRepository<GroupInfo, String> {
@EntityGraph(attributePaths = { "members" })
GroupInfo getByGroupName(String name);
}
5.3.11. Projections
Spring Data query methods usually return one or multiple instances of the aggregate root managed by the repository. However, it might sometimes be desirable to create projections based on certain attributes of those types. Spring Data allows modeling dedicated return types, to more selectively retrieve partial views of the managed aggregates.
Imagine a repository and aggregate root type such as the following example:
class Person {
@Id UUID id;
String firstname, lastname;
Address address;
static class Address {
String zipCode, city, street;
}
}
interface PersonRepository extends Repository<Person, UUID> {
Collection<Person> findByLastname(String lastname);
}
Now imagine that we want to retrieve the person’s name attributes only. What means does Spring Data offer to achieve this? The rest of this chapter answers that question.
Interface-based Projections
The easiest way to limit the result of the queries to only the name attributes is by declaring an interface that exposes accessor methods for the properties to be read, as shown in the following example:
interface NamesOnly {
String getFirstname();
String getLastname();
}
The important bit here is that the properties defined here exactly match properties in the aggregate root. Doing so lets a query method be added as follows:
interface PersonRepository extends Repository<Person, UUID> {
Collection<NamesOnly> findByLastname(String lastname);
}
The query execution engine creates proxy instances of that interface at runtime for each element returned and forwards calls to the exposed methods to the target object.
Projections can be used recursively. If you want to include some of the Address
information as well, create a projection interface for that and return that interface from the declaration of getAddress()
, as shown in the following example:
interface PersonSummary {
String getFirstname();
String getLastname();
AddressSummary getAddress();
interface AddressSummary {
String getCity();
}
}
On method invocation, the address
property of the target instance is obtained and wrapped into a projecting proxy in turn.
Closed Projections
A projection interface whose accessor methods all match properties of the target aggregate is considered to be a closed projection. The following example (which we used earlier in this chapter, too) is a closed projection:
interface NamesOnly {
String getFirstname();
String getLastname();
}
If you use a closed projection, Spring Data can optimize the query execution, because we know about all the attributes that are needed to back the projection proxy. For more details on that, see the module-specific part of the reference documentation.
Open Projections
Accessor methods in projection interfaces can also be used to compute new values by using the @Value
annotation, as shown in the following example:
interface NamesOnly {
@Value("#{target.firstname + ' ' + target.lastname}")
String getFullName();
…
}
The aggregate root backing the projection is available in the target
variable.
A projection interface using @Value
is an open projection.
Spring Data cannot apply query execution optimizations in this case, because the SpEL expression could use any attribute of the aggregate root.
The expressions used in @Value
should not be too complex — you want to avoid programming in String
variables.
For very simple expressions, one option might be to resort to default methods (introduced in Java 8), as shown in the following example:
interface NamesOnly {
String getFirstname();
String getLastname();
default String getFullName() {
return getFirstname.concat(" ").concat(getLastname());
}
}
This approach requires you to be able to implement logic purely based on the other accessor methods exposed on the projection interface. A second, more flexible, option is to implement the custom logic in a Spring bean and then invoke that from the SpEL expression, as shown in the following example:
@Component
class MyBean {
String getFullName(Person person) {
…
}
}
interface NamesOnly {
@Value("#{@myBean.getFullName(target)}")
String getFullName();
…
}
Notice how the SpEL expression refers to myBean
and invokes the getFullName(…)
method and forwards the projection target as a method parameter.
Methods backed by SpEL expression evaluation can also use method parameters, which can then be referred to from the expression.
The method parameters are available through an Object
array named args
. The following example shows how to get a method parameter from the args
array:
interface NamesOnly {
@Value("#{args[0] + ' ' + target.firstname + '!'}")
String getSalutation(String prefix);
}
Again, for more complex expressions, you should use a Spring bean and let the expression invoke a method, as described earlier.
Class-based Projections (DTOs)
Another way of defining projections is by using value type DTOs (Data Transfer Objects) that hold properties for the fields that are supposed to be retrieved. These DTO types can be used in exactly the same way projection interfaces are used, except that no proxying happens and no nested projections can be applied.
If the store optimizes the query execution by limiting the fields to be loaded, the fields to be loaded are determined from the parameter names of the constructor that is exposed.
The following example shows a projecting DTO:
class NamesOnly {
private final String firstname, lastname;
NamesOnly(String firstname, String lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
String getFirstname() {
return this.firstname;
}
String getLastname() {
return this.lastname;
}
// equals(…) and hashCode() implementations
}
Avoid boilerplate code for projection DTOs
You can dramatically simplify the code for a DTO by using Project Lombok, which provides an
Fields are |
Dynamic Projections
So far, we have used the projection type as the return type or element type of a collection. However, you might want to select the type to be used at invocation time (which makes it dynamic). To apply dynamic projections, use a query method such as the one shown in the following example:
interface PersonRepository extends Repository<Person, UUID> {
<T> Collection<T> findByLastname(String lastname, Class<T> type);
}
This way, the method can be used to obtain the aggregates as is or with a projection applied, as shown in the following example:
void someMethod(PersonRepository people) {
Collection<Person> aggregates =
people.findByLastname("Matthews", Person.class);
Collection<NamesOnly> aggregates =
people.findByLastname("Matthews", NamesOnly.class);
}
5.4. Stored Procedures
The JPA 2.1 specification introduced support for calling stored procedures by using the JPA criteria query API. We Introduced the @Procedure
annotation for declaring stored procedure metadata on a repository method.
The examples to follow use the following procedure:
plus1inout
procedure in HSQL DB./;
DROP procedure IF EXISTS plus1inout
/;
CREATE procedure plus1inout (IN arg int, OUT res int)
BEGIN ATOMIC
set res = arg + 1;
END
/;
Metadata for stored procedures can be configured by using the NamedStoredProcedureQuery
annotation on an entity type.
@Entity
@NamedStoredProcedureQuery(name = "User.plus1", procedureName = "plus1inout", parameters = {
@StoredProcedureParameter(mode = ParameterMode.IN, name = "arg", type = Integer.class),
@StoredProcedureParameter(mode = ParameterMode.OUT, name = "res", type = Integer.class) })
public class User {}
You can reference stored procedures from a repository method in multiple ways. The stored procedure to be called can either be defined directly by using the value
or procedureName
attribute of the @Procedure
annotation or indirectly by using the name
attribute. If no name is configured, the name of the repository method is used as a fallback.
The following example shows how to reference an explicitly mapped procedure:
@Procedure("plus1inout")
Integer explicitlyNamedPlus1inout(Integer arg);
The following example shows how to reference an implicitly mapped procedure by using a procedureName
alias:
procedureName
alias.@Procedure(procedureName = "plus1inout")
Integer plus1inout(Integer arg);
The following example shows how to reference an explicitly mapped named procedure in EntityManager
:
EntityManager
.@Procedure(name = "User.plus1IO")
Integer entityAnnotatedCustomNamedProcedurePlus1IO(@Param("arg") Integer arg);
The following example shows how to reference an implicitly named stored procedure in EntityManager
by using the method name:
EntityManager
by using the method name.@Procedure
Integer plus1(@Param("arg") Integer arg);
5.5. Specifications
JPA 2 introduces a criteria API that you can use to build queries programmatically. By writing a criteria
, you define the where clause of a query for a domain class. Taking another step back, these criteria can be regarded as a predicate over the entity that is described by the JPA criteria API constraints.
Spring Data JPA takes the concept of a specification from Eric Evans' book, “Domain Driven Design”, following the same semantics and providing an API to define such specifications with the JPA criteria API. To support specifications, you can extend your repository interface with the JpaSpecificationExecutor
interface, as follows:
public interface CustomerRepository extends CrudRepository<Customer, Long>, JpaSpecificationExecutor {
…
}
The additional interface has methods that let you execute specifications in a variety of ways. For example, the findAll
method returns all entities that match the specification, as shown in the following example:
List<T> findAll(Specification<T> spec);
The Specification
interface is defined as follows:
public interface Specification<T> {
Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
CriteriaBuilder builder);
}
Specifications can easily be used to build an extensible set of predicates on top of an entity that then can be combined and used with JpaRepository
without the need to declare a query (method) for every needed combination, as shown in the following example:
public class CustomerSpecs {
public static Specification<Customer> isLongTermCustomer() {
return new Specification<Customer>() {
public Predicate toPredicate(Root<Customer> root, CriteriaQuery<?> query,
CriteriaBuilder builder) {
LocalDate date = new LocalDate().minusYears(2);
return builder.lessThan(root.get(_Customer.createdAt), date);
}
};
}
public static Specification<Customer> hasSalesOfMoreThan(MontaryAmount value) {
return new Specification<Customer>() {
public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
CriteriaBuilder builder) {
// build query here
}
};
}
}
Admittedly, the amount of boilerplate leaves room for improvement (that may eventually be reduced by Java 8 closures), but the client side becomes much nicer, as you will see later in this section. The _Customer
type is a metamodel type generated using the JPA Metamodel generator (see the Hibernate implementation’s documentation for an example). So the expression, _Customer.createdAt
, assumes the Customer
has a createdAt
attribute of type Date
. Besides that, we have expressed some criteria on a business requirement abstraction level and created executable Specifications
. So a client might use a Specification
as follows:
List<Customer> customers = customerRepository.findAll(isLongTermCustomer());
Why not create a query for this kind of data access? Using a single Specification
does not gain a lot of benefit over a plain query declaration. The power of specifications really shines when you combine them to create new Specification
objects. You can achieve this through the Specifications
helper class we provide to build expressions similar to the following:
MonetaryAmount amount = new MonetaryAmount(200.0, Currencies.DOLLAR);
List<Customer> customers = customerRepository.findAll(
where(isLongTermCustomer()).or(hasSalesOfMoreThan(amount)));
Specifications
offers some “glue-code” methods to chain and combine Specification
instances. These methods let you extend your data access layer by creating new Specification
implementations and combining them with already existing implementations.
5.6. Query by Example
5.6.1. Introduction
This chapter provides an introduction to Query by Example and explains how to use it.
Query by Example (QBE) is a user-friendly querying technique with a simple interface. It allows dynamic query creation and does not require you to write queries that contain field names. In fact, Query by Example does not require you to write queries by using store-specific query languages at all.
5.6.2. Usage
The Query by Example API consists of three parts:
-
Probe: The actual example of a domain object with populated fields.
-
ExampleMatcher
: TheExampleMatcher
carries details on how to match particular fields. It can be reused across multiple Examples. -
Example
: AnExample
consists of the probe and theExampleMatcher
. It is used to create the query.
Query by Example is well suited for several use cases:
-
Querying your data store with a set of static or dynamic constraints.
-
Frequent refactoring of the domain objects without worrying about breaking existing queries.
-
Working independently from the underlying data store API.
Query by Example also has several limitations:
-
No support for nested or grouped property constraints, such as
firstname = ?0 or (firstname = ?1 and lastname = ?2)
. -
Only supports starts/contains/ends/regex matching for strings and exact matching for other property types.
Before getting started with Query by Example, you need to have a domain object. To get started, create an interface for your repository, as shown in the following example:
public class Person {
@Id
private String id;
private String firstname;
private String lastname;
private Address address;
// … getters and setters omitted
}
The preceding example shows a simple domain object. You can use it to create an Example
. By default, fields having null
values are ignored, and strings are matched by using the store specific defaults. Examples can be built by either using the of
factory method or by using ExampleMatcher
. Example
is immutable. The following listing shows a simple Example:
Person person = new Person(); (1)
person.setFirstname("Dave"); (2)
Example<Person> example = Example.of(person); (3)
1 | Create a new instance of the domain object. |
2 | Set the properties to query. |
3 | Create the Example . |
Examples are ideally be executed with repositories. To do so, let your repository interface extend QueryByExampleExecutor<T>
. The following listing shows an excerpt from the QueryByExampleExecutor
interface:
QueryByExampleExecutor
public interface QueryByExampleExecutor<T> {
<S extends T> S findOne(Example<S> example);
<S extends T> Iterable<S> findAll(Example<S> example);
// … more functionality omitted.
}
You can read more about Query by Example Execution below.
5.6.3. Example Matchers
Examples are not limited to default settings. You can specify your own defaults for string matching, null handling, and property-specific settings by using the ExampleMatcher
, as shown in the following example:
Person person = new Person(); (1)
person.setFirstname("Dave"); (2)
ExampleMatcher matcher = ExampleMatcher.matching() (3)
.withIgnorePaths("lastname") (4)
.withIncludeNullValues() (5)
.withStringMatcherEnding(); (6)
Example<Person> example = Example.of(person, matcher); (7)
1 | Create a new instance of the domain object. |
2 | Set properties. |
3 | Create an ExampleMatcher to expect all values to match. It is usable at this stage even without further configuration. |
4 | Construct a new ExampleMatcher to ignore the lastname property path. |
5 | Construct a new ExampleMatcher to ignore the lastname property path and to include null values. |
6 | Construct a new ExampleMatcher to ignore the lastname property path, to include null values, and to perform suffix string matching. |
7 | Create a new Example based on the domain object and the configured ExampleMatcher . |
By default, the ExampleMatcher
expects all values set on the probe to match. If you want to get results matching any of the predicates defined implicitly, use ExampleMatcher.matchingAny()
.
You can specify behavior for individual properties (such as "firstname" and "lastname" or, for nested properties, "address.city"). You can tune it with matching options and case sensitivity, as shown in the following example:
ExampleMatcher matcher = ExampleMatcher.matching()
.withMatcher("firstname", endsWith())
.withMatcher("lastname", startsWith().ignoreCase());
}
Another way to configure matcher options is to use lambdas (introduced in Java 8). This approach creates a callback that asks the implementor to modify the matcher. You need not return the matcher, because configuration options are held within the matcher instance. The following example shows a matcher that uses lambdas:
ExampleMatcher matcher = ExampleMatcher.matching()
.withMatcher("firstname", match -> match.endsWith())
.withMatcher("firstname", match -> match.startsWith());
}
Queries created by Example
use a merged view of the configuration. Default matching settings can be set at the ExampleMatcher
level, while individual settings can be applied to particular property paths. Settings that are set on ExampleMatcher
are inherited by property path settings unless they are defined explicitly. Settings on a property patch have higher precedence than default settings. The following table describes the scope of the various ExampleMatcher
settings:
Setting | Scope |
---|---|
Null-handling |
|
String matching |
|
Ignoring properties |
Property path |
Case sensitivity |
|
Value transformation |
Property path |
5.6.4. Executing an example
In Spring Data JPA, you can use Query by Example with Repositories, as shown in the following example:
public interface PersonRepository extends JpaRepository<Person, String> { … }
public class PersonService {
@Autowired PersonRepository personRepository;
public List<Person> findPeople(Person probe) {
return personRepository.findAll(Example.of(probe));
}
}
Currently, only SingularAttribute properties can be used for property matching.
|
The property specifier accepts property names (such as firstname
and lastname
). You can navigate by chaining properties together with dots (address.city
). You can also tune it with matching options and case sensitivity.
The following table shows the various StringMatcher
options that you can use and the result of using them on a field named firstname
:
Matching | Logical result |
---|---|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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5.7. Transactionality
By default, CRUD methods on repository instances are transactional. For read operations, the transaction configuration readOnly
flag is set to true
. All others are configured with a plain @Transactional
so that default transaction configuration applies. For details, see JavaDoc of SimpleJpaRepository
. If you need to tweak transaction configuration for one of the methods declared in a repository, redeclare the method in your repository interface, as follows:
public interface UserRepository extends CrudRepository<User, Long> {
@Override
@Transactional(timeout = 10)
public List<User> findAll();
// Further query method declarations
}
Doing so causes the findAll()
method to run with a timeout of 10 seconds and without the readOnly
flag.
Another way to alter transactional behaviour is to use a facade or service implementation that (typically) covers more than one repository. Its purpose is to define transactional boundaries for non-CRUD operations. The following example shows how to use such a facade for more than one repository:
@Service
class UserManagementImpl implements UserManagement {
private final UserRepository userRepository;
private final RoleRepository roleRepository;
@Autowired
public UserManagementImpl(UserRepository userRepository,
RoleRepository roleRepository) {
this.userRepository = userRepository;
this.roleRepository = roleRepository;
}
@Transactional
public void addRoleToAllUsers(String roleName) {
Role role = roleRepository.findByName(roleName);
for (User user : userRepository.findAll()) {
user.addRole(role);
userRepository.save(user);
}
}
This example causes call to addRoleToAllUsers(…)
to run inside a transaction (participating in an existing one or creating a new one if none are already running). The transaction configuration at the repositories is then neglected, as the outer transaction configuration determines the actual one used. Note that you must activate <tx:annotation-driven />
or use @EnableTransactionManagement
explicitly to get annotation-based configuration of facades to work. This example assumes you use component scanning.
5.7.1. Transactional query methods
To let your query methods be transactional, use @Transactional
at the repository interface you define, as shown in the following example:
@Transactional(readOnly = true)
public interface UserRepository extends JpaRepository<User, Long> {
List<User> findByLastname(String lastname);
@Modifying
@Transactional
@Query("delete from User u where u.active = false")
void deleteInactiveUsers();
}
Typically, you want the readOnly
flag to be set to true
, as most of the query methods only read data. In contrast to that, deleteInactiveUsers()
makes use of the @Modifying
annotation and overrides the transaction configuration. Thus, the method runs with the readOnly
flag set to false
.
You can use transactions for read-only queries and mark them as such by setting the |
5.8. Locking
To specify the lock mode to be used, you can use the @Lock
annotation on query methods, as shown in the following example:
interface UserRepository extends Repository<User, Long> {
// Plain query method
@Lock(LockModeType.READ)
List<User> findByLastname(String lastname);
}
This method declaration causes the query being triggered to be equipped with a LockModeType
of READ
. You can also define locking for CRUD methods by redeclaring them in your repository interface and adding the @Lock
annotation, as shown in the following example:
interface UserRepository extends Repository<User, Long> {
// Redeclaration of a CRUD method
@Lock(LockModeType.READ);
List<User> findAll();
}
5.9. Auditing
5.9.1. Basics
Spring Data provides sophisticated support to transparently keep track of who created or changed an entity and when the change happened. To benefit from that functionality, you have to equip your entity classes with auditing metadata that can be defined either using annotations or by implementing an interface.
Annotation-based Auditing Metadata
We provide @CreatedBy
and @LastModifiedBy
to capture the user who created or modified the entity as well as @CreatedDate
and @LastModifiedDate
to capture when the change happened.
class Customer {
@CreatedBy
private User user;
@CreatedDate
private DateTime createdDate;
// … further properties omitted
}
As you can see, the annotations can be applied selectively, depending on which information you want to capture. The annotations capturing when changes were made can be used on properties of type Joda-Time, DateTime
, legacy Java Date
and Calendar
, JDK8 date and time types, and long
or Long
.
Interface-based Auditing Metadata
In case you do not want to use annotations to define auditing metadata, you can let your domain class implement the Auditable
interface. It exposes setter methods for all of the auditing properties.
There is also a convenience base class, AbstractAuditable
, which you can extend to avoid the need to manually implement the interface methods. Doing so increases the coupling of your domain classes to Spring Data, which might be something you want to avoid. Usually, the annotation-based way of defining auditing metadata is preferred as it is less invasive and more flexible.
AuditorAware
In case you use either @CreatedBy
or @LastModifiedBy
, the auditing infrastructure somehow needs to become aware of the current principal. To do so, we provide an AuditorAware<T>
SPI interface that you have to implement to tell the infrastructure who the current user or system interacting with the application is. The generic type T
defines what type the properties annotated with @CreatedBy
or @LastModifiedBy
have to be.
The following example shows an implementation of the interface that uses Spring Security’s Authentication
object:
class SpringSecurityAuditorAware implements AuditorAware<User> {
public User getCurrentAuditor() {
Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
if (authentication == null || !authentication.isAuthenticated()) {
return null;
}
return ((MyUserDetails) authentication.getPrincipal()).getUser();
}
}
The implementation accesses the Authentication
object provided by Spring Security and looks up the custom UserDetails
instance that you have created in your UserDetailsService
implementation. We assume here that you are exposing the domain user through the UserDetails
implementation but that, based on the Authentication
found, you could also look it up from anywhere.
:leveloffset: -1
5.9.2. JPA Auditing
General Auditing Configuration
Spring Data JPA ships with an entity listener that can be used to trigger the capturing of auditing information. First, you must register the AuditingEntityListener
to be used for all entities in your persistence contexts inside your orm.xml
file, as shown in the following example:
<persistence-unit-metadata>
<persistence-unit-defaults>
<entity-listeners>
<entity-listener class="….data.jpa.domain.support.AuditingEntityListener" />
</entity-listeners>
</persistence-unit-defaults>
</persistence-unit-metadata>
You can also enable the AuditingEntityListener
on a per-entity basis by using the @EntityListeners
annotation, as follows:
@Entity
@EntityListeners(AuditingEntityListener.class)
public class MyEntity {
}
The auditing feature requires spring-aspects.jar to be on the classpath.
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With orm.xml
suitably modified and spring-aspects.jar
on the classpath, activating auditing functionality is a matter of adding the Spring Data JPA auditing
namespace element to your configuration, as follows:
<jpa:auditing auditor-aware-ref="yourAuditorAwareBean" />
As of Spring Data JPA 1.5, you can enable auditing by annotating a configuration class with the @EnableJpaAuditing
annotation. You must still modify the orm.xml
file and have spring-aspects.jar
on the classpath. The following example shows how to use the @EnableJpaAuditing
annotation:
@Configuration
@EnableJpaAuditing
class Config {
@Bean
public AuditorAware<AuditableUser> auditorProvider() {
return new AuditorAwareImpl();
}
}
If you expose a bean of type AuditorAware
to the ApplicationContext
, the auditing infrastructure automatically picks it up and uses it to determine the current user to be set on domain types. If you have multiple implementations registered in the ApplicationContext
, you can select the one to be used by explicitly setting the auditorAwareRef
attribute of @EnableJpaAuditing
.
5.10. Miscellaneous Considerations
5.10.1. Using JpaContext
in Custom Implementations
When working with multiple EntityManager
instances and custom repository implementations, you need to wire the correct EntityManager
into the repository implementation class. You can do so by explicitly naming the EntityManager
in the @PersistenceContext
annotation or, if the EntityManager
is @Autowired
, by using @Qualifier
.
As of Spring Data JPA 1.9, Spring Data JPA includes a class called JpaContext
that lets you obtain the EntityManager
by managed domain class, assuming it is managed by only one of the EntityManager
instances in the application. The following example shows how to use JpaContext
in a custom repository:
JpaContext
in a custom repository implementationclass UserRepositoryImpl implements UserRepositoryCustom {
private final EntityManager em;
@Autowired
public UserRepositoryImpl(JpaContext context) {
this.em = context.getEntityManagerByManagedType(User.class);
}
…
}
The advantage of this approach is that, if the domain type gets assigned to a different persistence unit, the repository does not have to be touched to alter the reference to the persistence unit.
5.10.2. Merging persistence units
Spring supports having multiple persistence units. Sometimes, however, you might want to modularize your application but still make sure that all these modules run inside a single persistence unit. To enable that behavior, Spring Data JPA offers a PersistenceUnitManager
implementation that automatically merges persistence units based on their name, as shown in the following example:
<bean class="….LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitManager">
<bean class="….MergingPersistenceUnitManager" />
</property>
</bean>
Classpath Scanning for @Entity Classes and JPA Mapping Files
A plain JPA setup requires all annotation-mapped entity classes to be listed in orm.xml
. The same applies to XML mapping files. Spring Data JPA provides a ClasspathScanningPersistenceUnitPostProcessor
that gets a base package configured and optionally takes a mapping filename pattern. It then scans the given package for classes annotated with @Entity
or @MappedSuperclass
, loads the configuration files that match the filename pattern, and hands them to the JPA configuration. The post-processor must be configured as follows:
<bean class="….LocalContainerEntityManagerFactoryBean">
<property name="persistenceUnitPostProcessors">
<list>
<bean class="org.springframework.data.jpa.support.ClasspathScanningPersistenceUnitPostProcessor">
<constructor-arg value="com.acme.domain" />
<property name="mappingFileNamePattern" value="**/*Mapping.xml" />
</bean>
</list>
</property>
</bean>
As of Spring 3.1, a package to scan can be configured on the LocalContainerEntityManagerFactoryBean directly to enable classpath scanning for entity classes. See the JavaDoc for details.
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5.10.3. CDI Integration
Instances of the repository interfaces are usually created by a container, for which Spring is the most natural choice when working with Spring Data. Spring offers sophisticated support for creating bean instances, as documented in Creating Repository Instances. As of version 1.1.0, Spring Data JPA ships with a custom CDI extension that allows using the repository abstraction in CDI environments. The extension is part of the JAR. To activate it, include the Spring Data JPA JAR on your classpath.
You can now set up the infrastructure by implementing a CDI Producer for the EntityManagerFactory
and EntityManager
, as shown in the following example:
class EntityManagerFactoryProducer {
@Produces
@ApplicationScoped
public EntityManagerFactory createEntityManagerFactory() {
return Persistence.createEntityManagerFactory("my-presistence-unit");
}
public void close(@Disposes EntityManagerFactory entityManagerFactory) {
entityManagerFactory.close();
}
@Produces
@RequestScoped
public EntityManager createEntityManager(EntityManagerFactory entityManagerFactory) {
return entityManagerFactory.createEntityManager();
}
public void close(@Disposes EntityManager entityManager) {
entityManager.close();
}
}
The necessary setup can vary depending on the JavaEE environment. You may need to do nothing more than redeclare a EntityManager
as a CDI bean, as follows:
class CdiConfig {
@Produces
@RequestScoped
@PersistenceContext
public EntityManager entityManager;
}
In the preceding example, the container has to be capable of creating JPA EntityManagers
itself. All the configuration does is re-export the JPA EntityManager
as a CDI bean.
The Spring Data JPA CDI extension picks up all available EntityManager
instances as CDI beans and creates a proxy for a Spring Data repository whenever a 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 @Injected
property, as shown in the following example:
class RepositoryClient {
@Inject
PersonRepository repository;
public void businessMethod() {
List<Person> people = repository.findAll();
}
}
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. See “XML configuration”. The following table describes the attributes of the <repositories />
element:
Name | Description |
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Defines the package to be scanned for repository interfaces that extend |
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Defines the postfix to autodetect custom repository implementations. Classes whose names end with the configured postfix are considered as candidates. Defaults to |
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Determines the strategy to be used to create finder queries. See “Query Lookup Strategies” for details. Defaults to |
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Defines the location to search for a Properties file containing externally defined queries. |
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Whether nested repository interface definitions should be considered. Defaults to |
Appendix B: Populators namespace reference
The <populator /> element
The <populator />
element allows to populate the a data store via the Spring Data repository infrastructure.[1]
Name | Description |
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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 keywords listed here might not be supported in a particular store.
Logical keyword | Keyword expressions |
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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 types listed here might not be supported in a particular store.
Geospatial types (such as GeoResult , GeoResults , and GeoPage ) are available only for data stores that support geospatial queries.
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Return type | Description |
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Denotes no return value. |
Primitives |
Java primitives. |
Wrapper types |
Java wrapper types. |
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An unique entity. Expects the query method to return one result at most. If no result is found, |
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An |
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A |
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A |
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A Java 8 or Guava |
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Either a Scala or Javaslang |
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A Java 8 |
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A |
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A Java 8 |
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A |
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A sized chunk of data with an indication of whether there is more data available. Requires a |
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A |
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A result entry with additional information, such as the distance to a reference location. |
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A list of |
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A |
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A Project Reactor |
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A Project Reactor |
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A RxJava |
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A RxJava |
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A RxJava |
Appendix E: Frequently Asked Questions
Common
-
I’d like to get more detailed logging information on what methods are called inside
JpaRepository
(for exmaple). How can I gain them?You can make use of
CustomizableTraceInterceptor
provided by Spring, as shown in the following example:<bean id="customizableTraceInterceptor" class=" org.springframework.aop.interceptor.CustomizableTraceInterceptor"> <property name="enterMessage" value="Entering $[methodName]($[arguments])"/> <property name="exitMessage" value="Leaving $[methodName](): $[returnValue]"/> </bean> <aop:config> <aop:advisor advice-ref="customizableTraceInterceptor" pointcut="execution(public * org.springframework.data.jpa.repository.JpaRepository+.*(..))"/> </aop:config>
Infrastructure
-
Currently I have implemented a repository layer based on
HibernateDaoSupport
. I create aSessionFactory
by using Spring’sAnnotationSessionFactoryBean
. How do I get Spring Data repositories working in this environment?You have to replace
AnnotationSessionFactoryBean
with theHibernateJpaSessionFactoryBean
, as follows:Example 104. Looking up aSessionFactory
from aHibernateEntityManagerFactory
<bean id="sessionFactory" class="org.springframework.orm.jpa.vendor.HibernateJpaSessionFactoryBean"> <property name="entityManagerFactory" ref="entityManagerFactory"/> </bean>
Appendix F: Glossary
- AOP
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Aspect oriented programming
- Commons DBCP
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Commons DataBase Connection Pools - a library from the Apache foundation that offers pooling implementations of the DataSource interface.
- CRUD
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Create, Read, Update, Delete - Basic persistence operations.
- DAO
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Data Access Object - Pattern to separate persisting logic from the object to be persisted
- Dependency Injection
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Pattern to hand a component’s dependency to the component from outside, freeing the component to lookup the dependent itself. For more information, see http://en.wikipedia.org/wiki/Dependency_Injection.
- EclipseLink
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Object relational mapper implementing JPA - http://www.eclipselink.org
- Hibernate
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Object relational mapper implementing JPA - http://www.hibernate.org
- JPA
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Java Persistence API
- Spring
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Java application framework - http://projects.spring.io/spring-framework