On behalf of the team and everyone that contributed, I am pleased to announce that the first release candidate of Spring Data R2DBC 1.0 has been released and is available from our milestone repository. This release contains 60 issues and pull requests. It upgrades its baseline to R2DBC 0.8 RC1 and Spring Data Moore GA.

The most notable features are:

• ConnectionFactory routing through AbstractRoutingConnectionFactory.
• Utilities for schema initialization through ResourceDatabasePopulator and ScriptUtils.
• Propagation and reset of Auto-Commit and Isolation Level control through TransactionDefinition.
• Support for Entity-level converters.
• Kotlin extensions for reified generics and Coroutines.
• Add pluggable mechanism to register dialects.
• API refinements.

ConnectionFactory Routing

For each operation, DatabaseClient obtains a Connection from the ConnectionFactory that is used to create DatabaseClient.

The general idea is that a routing ConnectionFactory acts as an intermediary - while the ‘real’ ConnectionFactory is determined dynamically at runtime based on a lookup key. One potential use case is for catering to multi-tenancy by using multiple ConnectionFactory instances that point to a separate database. For a routing ConnectionFactory to determine which ConnectionFactory to use, it requires contextual information. Spring Data R2DBC comes with an AbstractRoutingConnectionFactory that can return a lookup key that is used to look up the right ConnectionFactory.

Reactive flows can attach contextual information to the subscription by using Project Reactor's Context.

An example implementation for a routing ConnectionFactory might look like the following listing:

class RoutingConnectionFactory extends AbstractRoutingConnectionFactory {

    public static final String ROUTING_KEY = "routing-key";

    @Override
    protected Mono<Object> determineCurrentLookupKey() {
        return Mono.subscriberContext().filter(it -> it.hasKey(ROUTING_KEY)).map(it -> it.get(ROUTING_KEY));
    }
}

The following listing shows how to initialize the connection factory a map between the lookup key and the target ConnectionFactory:

RoutingConnectionFactory connectionFactory = new RoutingConnectionFactory();
Map<String, ConnectionFactory> factories = new HashMap<>();
factories.put("customer1", …);
factories.put("customer2", …);
connectionFactory.setTargetConnectionFactories(factories);
connectionFactory.afterPropertiesSet();

You can create a DatabaseClient by using the routing ConnectionFactory to determine the appropriate ConnectionFactory for each subscription. The routing key itself gets attached to the Context and is evaluated by RoutingConnectionFactory, as the following listing shows:

DatabaseClient client = DatabaseClient.create(connectionFactory);

Context routingContext = Context.of(ROUTING_KEY, "customer1");

Flux<User> users = client.execute("SELECT first_name, last_name FROM user")
                .as(User.class)
                .fetch()
                .all()
                .subscriberContext(routingContext);

Schema Initialization

The org.springframework.data.r2dbc.connectionfactory.init package provides support for initializing an existing ConnectionFactory. You may sometimes need to initialize an instance that runs on a server somewhere or that is an embedded database. The following listing shows how to register and configure a ConnectionFactoryInitializer bean to initialize your database through a ConnectionFactory.

@Configuration
public class InitializerConfiguration {

  @Bean
  public ConnectionFactoryInitializer initializer(ConnectionFactory connectionFactory) {

    ConnectionFactoryInitializer initializer = new ConnectionFactoryInitializer();
    initializer.setConnectionFactory(connectionFactory);

    CompositeDatabasePopulator populator = new CompositeDatabasePopulator();
    populator.addPopulators(new ResourceDatabasePopulator(new ClassPathResource("com/foo/sql/db-schema.sql")));
    populator.addPopulators(new ResourceDatabasePopulator(new ClassPathResource("com/foo/sql/test-data1.sql")));
    initializer.setDatabasePopulator(populator);

    return initializer;
  }
}

This initialization support is used by Spring Boot R2DBC auto-configuration to apply schema.sql and data.sql to the configured ConnectionFactory.

Kotlin Extensions

This release ships with Kotlin extensions for idiomatic usage of Spring Data R2DBC when developing applications with Kotlin.

Spring Data R2DBC provides the following extensions:

• Reified generics support for DatabaseClient and Criteria
• Kotlin Coroutines support for DatabaseClient

To retrieve a list of User objects in Java, you would normally write the following:

Flux<User> characters = client.select().from(User.class).fetch().all();

With Kotlin and the Spring Data extensions, you can instead write the following:

val users =  client.select().from<User>().fetch().all()

Kotlin Coroutines are Kotlin lightweight threads that allow writing non-blocking code in an imperative style. Spring Data R2DBC's Coroutines extensions leverages the reactive infrastructure to expose functions you can suspend and bridge Flux results into Kotlin's Flow type.

The following example shows Coroutine usage with Spring Framework's TransactionalOperator to atomically insert two rows:

operator.executeAndAwait {
  client.execute("INSERT INTO person VALUES(:first_name, :last_name)")
        .bind("first_name", "John")
        .bind("last_name", "Doe")
        .await()
  client.execute("INSERT INTO person_events VALUES(:first_name, :last_name, :event_type)")
        .bind("first_name", "John")
        .bind("last_name", "Doe")
        .bind("event_type", "CREATED")
        .await()
}

Note that most suspend methods end with await, as an indicator for Coroutines methods.

Pluggable Dialects

As of now, the R2DBC driver eco-system consists of only a few known drivers, but the number of drivers is growing. To enable seamless integration with additional drivers, Spring Data R2DBC exposes an extension point for R2dbcDialect registration. Spring Data R2DBC can auto-discover a R2dbcDialect by registering a class that implements org.springframework.data.r2dbc.dialect.DialectResolver$R2dbcDialectProvider through Spring's META-INF/spring.factories mechanism. The following listing shows how to do so:

public class MyDialectProvider implements DialectResolver.R2dbcDialectProvider {

    @Override
    public Optional<R2dbcDialect> getDialect(ConnectionFactory connectionFactory) {

        if (connectionFactory.getMetadata().getName().equals("my-dastabase")) {
            return Optional.of(…);
        }
        return Optional.empty();
    }
}

spring.factories

org.springframework.data.r2dbc.dialect.DialectResolver$R2dbcDialectProvider=com.example.MyDialectProvider

Artifact Coordinates

If you use Maven, add the following lines to your pom.xml file to upgrade to Spring Data R2DBC 1.0 RC1:

<dependencies>
  <dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-r2dbc</artifactId>
    <version>1.0.0.RC1</version>
  </dependency>
</dependencies>

<!-- R2DBC 0.8.0.RC1 required -->
<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>io.r2dbc</groupId>
      <artifactId>r2dbc-bom</artifactId>
      <version>Arabba-RC1</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<repositories>
  <repository>
    <id>spring-milestone</id>
    <url>https://repo.spring.io/milestone</url>
  </repository>
</repositories>

Next steps

R2DBC 0.8.0 RC1 was recently released, and we expect a GA release later this year. We're working towards a Spring Data R2DBC 1.0 GA release and will ship the next release once R2DBC itself is GA. Our backlog contains a series of enhancements, such as query derivation, optimistic locking, and allowing for query interception to alter bindings and SQL statements before they get executed.

To round things off, here are links to the changelog, GitHub repository, and docs:

• Project Repository: github.com/spring-projects/spring-data-r2dbc
• Issue Tracker: github.com/spring-projects/spring-data-r2dbc/issues
• Artifacts - Javadoc - Documentation - Changelog