Cassandra Repositories

To access domain entities stored in Apache Cassandra, you can use Spring Data’s sophisticated repository support, which significantly eases implementing DAOs. To do so, create an interface for your repository, as the following example shows:

Example 1. Sample Person entity

@Table
public class Person {

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

  // … getters and setters omitted
}

Note that the entity has a property named id of type String. The default conversion mechanism used in MappingCassandraConverter (which backs the repository support) regards properties named id as being the row ID.

The following example shows a repository definition to persist Person entities:

Basic repository interface to persist Person entities

Imperative
Reactive

interface PersonRepository extends CrudRepository<Person, String> {

  // additional custom finder methods go here
}

interface PersonRepository extends ReactiveCrudRepository<Person, String> {

  // additional custom finder methods go here
}

Right now, the interface in the preceding example serves only typing purposes, but we add additional methods to it later.

Next, in your Spring configuration, add the following (if you use Java for configuration):

If you want to use Java configuration, use the @EnableCassandraRepositories respective @EnableReactiveCassandraRepositories annotation. The annotation carries the same attributes as the namespace element. If no base package is configured, the infrastructure scans the package of the annotated configuration class. The following example show how to the different configuration approaches:

Configuration for repositories

Imperative Java Configuration
XML
Reactive Java Configuration

@Configuration
@EnableCassandraRepositories
class ApplicationConfig extends AbstractCassandraConfiguration {

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

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

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

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

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

    <cassandra:converter/>

    <cassandra:template/>

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

@Configuration
@EnableReactiveCassandraRepositories
class ApplicationConfig extends AbstractReactiveCassandraConfiguration {

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

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

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

Because our domain repository extends CrudRepository respective ReactiveCrudRepository, it provides you with basic CRUD operations. Working with the repository instance is a matter of injecting the repository as a dependency into a client, as the following example does by autowiring PersonRepository:

Basic access to Person entities

Imperative
Reactive

@ExtendWith(SpringExtension.class)
class PersonRepositoryTests {

    @Autowired PersonRepository repository;

    @Test
    void readsPersonTableCorrectly() {

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

public class PersonRepositoryTests {

    @Autowired ReactivePersonRepository repository;

    @Test
    public void sortsElementsCorrectly() {
        Flux<Person> people = repository.findAll(Sort.by(new Order(ASC, "lastname")));
    }
}

Cassandra repositories support paging and sorting for paginated and sorted access to the entities. Cassandra paging requires a paging state to forward-only navigate through pages. A Slice keeps track of the current paging state and allows for creation of a Pageable to request the next page. The following example shows how to set up paging access to Person entities:

Paging access to Person entities

Imperative
Reactive

@ExtendWith(SpringExtension.class)
class PersonRepositoryTests {

    @Autowired PersonRepository repository;

    @Test
    void readsPagesCorrectly() {

      Slice<Person> firstBatch = repository.findAll(CassandraPageRequest.first(10));

      assertThat(firstBatch).hasSize(10);

      Slice<Person> nextBatch = repository.findAll(firstBatch.nextPageable());

      // …
    }
}

@ExtendWith(SpringExtension.class)
class PersonRepositoryTests {

    @Autowired PersonRepository repository;

    @Test
    void readsPagesCorrectly() {

      Mono<Slice<Person>> firstBatch = repository.findAll(CassandraPageRequest.first(10));

      Mono<Slice<Person>> nextBatch = firstBatch.flatMap(it -> repository.findAll(it.nextPageable()));

      // …
    }
}}

Cassandra repositories do not extend PagingAndSortingRepository, because classic paging patterns using limit/offset are not applicable to Cassandra.

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

Reactive Repositories

Spring Data’s repository abstraction is a dynamic API that is mostly defined by you and your requirements as you declare query methods. Reactive Cassandra repositories can be implemented by using either RxJava or Project Reactor wrapper types by extending from one of the library-specific repository interfaces:

ReactiveCrudRepository
ReactiveSortingRepository
RxJava3CrudRepository
RxJava3SortingRepository

Spring Data converts reactive wrapper types behind the scenes so that you can stick to your favorite composition library.