Getting Started

An easy way to bootstrap setting up a working environment is to create a Spring-based project in Spring Tools or from Spring Initializr.

First, you need to set up a running database server. Refer to your vendor documentation on how to configure your database for R2DBC access.

Requirements

Spring Data R2DBC requires Spring Framework 6.2.0 and above.

In terms of databases, Spring Data R2DBC requires a driver to abstract common SQL functionality over vendor-specific flavours. Spring Data R2DBC includes direct support for the following databases:

If you use a different database then your application won’t start up. The dialect section contains further detail on how to proceed in such case.

Hello World

To create a Spring project in STS:

  1. Go to File → New → Spring Template Project → Simple Spring Utility Project, and press Yes when prompted. Then enter a project and a package name, such as org.spring.r2dbc.example.

  2. Add the following to the pom.xml files dependencies element:

  3. Add the following to the pom.xml files dependencies element:

    <dependencies>

  <!-- other dependency elements omitted -->

  <dependency>
    <groupId>org.springframework.data</groupId>
    <artifactId>spring-data-r2dbc</artifactId>
    <version>3.4.0</version>
  </dependency>

  <!-- a R2DBC driver -->
  <dependency>
    <groupId>io.r2dbc</groupId>
    <artifactId>r2dbc-h2</artifactId>
    <version>x.y.z</version>
  </dependency>

</dependencies>

  4. Change the version of Spring in the pom.xml to be

    <spring.version>6.2.0</spring.version>

  5. Add the following location of the Spring Milestone repository for Maven to your pom.xml such that it is at the same level as your <dependencies/> element:

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

The repository is also browseable here.

You may also want to set the logging level to DEBUG to see some additional information. To do so, edit the application.properties file to have the following content:

logging.level.org.springframework.r2dbc=DEBUG

Then you can, for example, create a Person class to persist, as follows:

public class Person {

	private final String id;
	private final String name;
	private final int age;

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

	public String getId() {
		return id;
	}

	public String getName() {
		return name;
	}

	public int getAge() {
		return age;
	}

	@Override
	public String toString() {
		return "Person [id=" + id + ", name=" + name + ", age=" + age + "]";
	}
}

Next, you need to create a table structure in your database, as follows:

CREATE TABLE person
  (id VARCHAR(255) PRIMARY KEY,
   name VARCHAR(255),
   age INT);

You also need a main application to run, as follows:

import io.r2dbc.spi.ConnectionFactories;
import io.r2dbc.spi.ConnectionFactory;
import reactor.test.StepVerifier;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.data.r2dbc.core.R2dbcEntityTemplate;

public class R2dbcApp {

  private static final Log log = LogFactory.getLog(R2dbcApp.class);

  public static void main(String[] args) {

    ConnectionFactory connectionFactory = ConnectionFactories.get("r2dbc:h2:mem:///test?options=DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE");

    R2dbcEntityTemplate template = new R2dbcEntityTemplate(connectionFactory);

    template.getDatabaseClient().sql("CREATE TABLE person" +
        "(id VARCHAR(255) PRIMARY KEY," +
        "name VARCHAR(255)," +
        "age INT)")
      .fetch()
      .rowsUpdated()
      .as(StepVerifier::create)
      .expectNextCount(1)
      .verifyComplete();

    template.insert(Person.class)
      .using(new Person("joe", "Joe", 34))
      .as(StepVerifier::create)
      .expectNextCount(1)
      .verifyComplete();

    template.select(Person.class)
      .first()
      .doOnNext(it -> log.info(it))
      .as(StepVerifier::create)
      .expectNextCount(1)
      .verifyComplete();
  }
}

When you run the main program, the preceding examples produce output similar to the following:

2018-11-28 10:47:03,893 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 310 - Executing SQL statement [CREATE TABLE person
  (id VARCHAR(255) PRIMARY KEY,
   name VARCHAR(255),
   age INT)]
2018-11-28 10:47:04,074 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 908 - Executing SQL statement [INSERT INTO person (id, name, age) VALUES($1, $2, $3)]
2018-11-28 10:47:04,092 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 575 - Executing SQL statement [SELECT id, name, age FROM person]
2018-11-28 10:47:04,436  INFO        org.spring.r2dbc.example.R2dbcApp:  43 - Person [id='joe', name='Joe', age=34]

Even in this simple example, there are few things to notice:

  • You can create an instance of the central helper class in Spring Data R2DBC (R2dbcEntityTemplate) by using a standard io.r2dbc.spi.ConnectionFactory object.

  • The mapper works against standard POJO objects without the need for any additional metadata (though you can, optionally, provide that information — see here.).

  • Mapping conventions can use field access.Notice that the Person class has only getters.

  • If the constructor argument names match the column names of the stored row, they are used to instantiate the object.

Examples Repository

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

Connecting to a Relational Database with Spring

One of the first tasks when using relational databases and Spring is to create a io.r2dbc.spi.ConnectionFactory object by using the IoC container. Make sure to use a supported database and driver.

Registering a ConnectionFactory Instance using Java Configuration

The following example shows an example of using Java-based bean metadata to register an instance of io.r2dbc.spi.ConnectionFactory:

Registering a io.r2dbc.spi.ConnectionFactory object using Java Configuration
@Configuration
public class ApplicationConfiguration extends AbstractR2dbcConfiguration {

  @Override
  @Bean
  public ConnectionFactory connectionFactory() {
    return …
  }
}

This approach lets you use the standard io.r2dbc.spi.ConnectionFactory instance, with the container using Spring’s AbstractR2dbcConfiguration.As compared to registering a ConnectionFactory instance directly, the configuration support has the added advantage of also providing the container with an ExceptionTranslator implementation that translates R2DBC exceptions to exceptions in Spring’s portable DataAccessException hierarchy for data access classes annotated with the @Repository annotation.This hierarchy and the use of @Repository is described in Spring’s DAO support features.

AbstractR2dbcConfiguration also registers DatabaseClient, which is required for database interaction and for Repository implementation.

Dialects

Spring Data R2DBC uses a Dialect to encapsulate behavior that is specific to a database or its driver. Spring Data R2DBC reacts to database specifics by inspecting the ConnectionFactory and selects the appropriate database dialect accordingly. If you use a database for which no dialect is available, then your application won’t start up. In that case, you’ll have to ask your vendor to provide a Dialect implementation. Alternatively, you can implement your own Dialect.

Dialects are resolved by DialectResolver from a ConnectionFactory, typically by inspecting ConnectionFactoryMetadata. + You can let Spring auto-discover your R2dbcDialect by registering a class that implements org.springframework.data.r2dbc.dialect.DialectResolver$R2dbcDialectProvider through META-INF/spring.factories. DialectResolver discovers dialect provider implementations from the class path using Spring’s SpringFactoriesLoader. To do so:

  1. Implement your own Dialect.

  2. Implement a R2dbcDialectProvider returning the Dialect.

  3. Register the provider by creating a spring.factories resource under META-INF and perform the registration by adding a line
    org.springframework.data.r2dbc.dialect.DialectResolver$R2dbcDialectProvider=<fully qualified name of your R2dbcDialectProvider>