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Spring Data 2020.0 - New and Noteworthy in Spring Data for Apache Cassandra 3.1

Spring Data 2020.0.0 ships with Spring Data for Apache Cassandra 3.1. This release ships with numerous enhancements that refine existing functionality and introduce support for selected Cassandra 4 features:

  • Reactive auditing
  • Reactive SpEL support in @Query query methods.
  • Configuration of the keyspace per Statement through CqlTemplate and QueryOptions.
  • Revised CqlOperations with new queryForStream(…) methods returning a Stream with transparent pagination.
  • DataClassRowMapper to map Cassandra results to data classes via constructor creation/bean properties

Reactive Auditing

Reactive auditing is enabled by annotating your configuration class with @EnableReactiveCassandraAuditing. Registering a bean that implements ReactiveAuditorAware serves as an interface to obtain the current auditor. The following example shows the required configuration:

@Configuration
@EnableReactiveCassandraAuditing  
class ApplicationConfiguration {  
  
  @Bean  
  ReactiveAuditorAware<String> reactiveAuditorAware() {  
      return …;
   }  
}

After enabling reactive auditing, you can use Spring Data’s auditing annotations in your domain class. If you have used Spring Data auditing before, then you may notice that there’s no difference in setting up the domain model compared to imperative usage of Spring Data.

public class Order implements Persistable<String> {  
    
   @Id String orderId;  
  
   @CreatedBy String createdBy;  
  
   @CreatedDate Instant createdDate;  
  
   @LastModifiedBy String lastModifiedBy;  
  
   @LastModifiedDate Instant lastModifiedDate;   
}

The domain class shown above refers to the auditor by using properties annotated with @CreatedBy and @LastModifiedBy. Properties that hold the creation or modification time are annotated with @CreatedDate or @LastModifiedDate, respectively.

You might have noticed that the domain class implements Persistable. To properly mark an entity as audited, Spring Data needs to know whether an entity is new or whether it should be considered to exist in the database. Typically, this happens by inspecting the @Id property to see whether it is null. Cassandra has no means to generate primary key values. New objects must be persisted with a provided identifier. Therefore, your domain model must express whether it should be considered new or existing (see Persistable.isNew()).
Alternatively, Spring Data can inspect the @Version property when using optimistic locking to tell whether an entity should be considered new.

You can use Reactive Auditing through reactive Cassandra repositories and through ReactiveCassandraTemplate.

A final note on the migration: With the introduction of reactive auditing, the entire reactive auditing infrastructure is registered only when your configuration is marked with @EnableReactiveCassandraAuditing. The previous version (3.0.x) registered a lightweight auditing called EntityCallback when @EnableCassandraAuditing was configured. That is no longer the case, so make sure to revisit your annotation-based configuration if you have previously used auditing features.

You can read more about auditing with Apache Cassandra in the Spring Data Cassandra reference documentation.

Keyspace configuration per Statement

Cassandra 4 allows specifying the target keyspace on a per-statement level. Instead of running statements in the logged keyspace, individual statements can target a different keyspace. To support this feature, Spring Data for Apache Cassandra allows configuration of the keyspace through:

  • CqlTemplate (including AsyncCqlTemplate and ReactiveCqlTemplate)
  • QueryOptions (including subclasses)

Configuring a keyspace on the Template API allows running all statements through a particular template on a different keyspace than the logged keyspace. A typical use case could be a keyspace per tenant model:

CqlSession cqlSession = …;  
CqlTemplate tenant1Template = new CqlTemplate(cqlSession);  
tenant1Template.setKeyspace(CqlIdentifier.fromCql("my-other-keyspace"));  
tenant1Template.queryForList("SELECT …");

CqlTemplate and its asynchronous and reactive variants are used by CassandraTemplate and the repository infrastructure, which allows wiring an entire stack to a different keyspace.

To customize the keyspace for individual operations on CassandraTemplate, you can use QueryOptions and its operation-specific subclasses to control the keyspace:

CassandraTemplate template = …;  
  
template.insert(person, InsertOptions.builder().keyspace("my-other-keyspace").build());

Note that this feature requires Cassandra 4, and it does not affect earlier Cassandra versions.

Revised CqlTemplate and asynchronous/reactive variants

With this release, we took the opportunity to refine our CQL Template API. For quite a while already, we wanted CqlTemplate to support Java 8 Stream, including transparent paging on CqlTemplate. Its reactive counterpart, ReactiveCqlTemplate, supported this feature with queryForFlux (since version 2.0). With this version, you can use queryForStream on CqlTemplate, allowing for lazy iteration over a java.util.stream.Stream:

CqlTemplate template = …;

Stream<String> stream = cqlTemplate.queryForStream("SELECT * from USERS", (row, index) -> row.getString(0));

Additionally, queryForStream serves CassandraTemplate.stream(…) to run queries that return a stream of entities.

The use of lightweight data classes and records (as of Java 15 and newer) becomes an increasingly popular choice for ad-hoc mapping of results. Instead of using the Entity-oriented CassandraTemplate, this release enables a more lightweight pattern to consume query results as plain Java beans, Kotlin data classes, and Java records. DataClassRowMapper is a dedicated RowMapper that instantiates classes following the data class/Java records pattern by inspecting their constructor properties. The following example illustrates Java Records usage:

record User(String id, String name, int age){}

CqlTemplate template = …;

Stream<User> stream = cqlTemplate.queryForStream("SELECT * from USERS", new DataClassRowMapper(User.class));

Here is the Kotlin data class variant:

data class User(id: String, name: String, age: Int)

val stream : Stream<Person> = cqlTemplate.queryForStream("SELECT * from USERS", DataClassRowMapper<User>())

You can use DataClassRowMapper with all CqlTemplate variants as all of these accept RowMapper.

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