To override the default settings just define a @Bean of your own of type DataSource. Spring Boot provides a utility builder class DataSourceBuilder that can be used to create one of the standard ones (if it is on the classpath), or you can just create your own, and bind it to a set of Environment properties e.g.

@Bean
@ConfigurationProperties(prefix="datasource.mine")
public DataSource dataSource() {
    return new FancyDataSource();
}

datasource.mine.jdbcUrl=jdbc:h2:mem:mydb
datasource.mine.user=sa
datasource.mine.poolSize=30

See 'Section 26.1, “Configure a DataSource”' in the ‘Spring Boot features’ section and the DataSourceAutoConfiguration class for more details.

Creating more than one data source works the same as creating the first one. You might want to mark one of them as @Primary if you are using the default auto-configuration for JDBC or JPA (then that one will be picked up by any @Autowired injections).

@Bean
@Primary
@ConfigurationProperties(prefix="datasource.primary")
public DataSource primaryDataSource() {
    return DataSourceBuilder.create().build();
}

@Bean
@ConfigurationProperties(prefix="datasource.secondary")
public DataSource secondaryDataSource() {
    return DataSourceBuilder.create().build();
}

Spring Data can create implementations for you of @Repository interfaces of various flavours. Spring Boot will handle all of that for you as long as those @Repositories are included in the same package (or a sub-package) of your @EnableAutoConfiguration class.

For many applications all you will need is to put the right Spring Data dependencies on your classpath (there is a spring-boot-starter-data-jpa for JPA and a spring-boot-starter-data-mongodb for Mongodb), create some repository interfaces to handle your @Entity objects. Examples are in the JPA sample or the Mongodb sample.

Spring Boot tries to guess the location of your @Repository definitions, based on the @EnableAutoConfiguration it finds. To get more control, use the @EnableJpaRepositories annotation (from Spring Data JPA).

Spring Boot tries to guess the location of your @Entity definitions, based on the @EnableAutoConfiguration it finds. To get more control, you can use the @EntityScan annotation, e.g.

@Configuration
@EnableAutoConfiguration
@EntityScan(basePackageClasses=City.class)
public class Application {

    //...

}

Spring Data JPA already provides some vendor-independent configuration options (e.g. for SQL logging) and Spring Boot exposes those, and a few more for hibernate as external configuration properties. The most common options to set are:

spring.jpa.hibernate.ddl-auto: create-drop
spring.jpa.hibernate.naming_strategy: org.hibernate.cfg.ImprovedNamingStrategy
spring.jpa.database: H2
spring.jpa.show-sql: true

(Because of relaxed data binding hyphens or underscores should work equally well as property keys.) The ddl-auto setting is a special case in that it has different defaults depending on whether you are using an embedded database (create-drop) or not (none). In addition all properties in spring.jpa.properties.* are passed through as normal JPA properties (with the prefix stripped) when the local EntityManagerFactory is created.

See HibernateJpaAutoConfiguration and JpaBaseConfiguration for more details.

To take full control of the configuration of the EntityManagerFactory, you need to add a @Bean named ‘entityManagerFactory’. Spring Boot auto-configuration switches off its entity manager based on the presence of a bean of that type.

Even if the default EntityManagerFactory works fine, you will need to define a new one because otherwise the presence of the second bean of that type will switch off the default. To make it easy to do that you can use the convenient EntityManagerBuilder provided by Spring Boot, or if you prefer you can just use the LocalContainerEntityManagerFactoryBean directly from Spring ORM.

Example:

// add two data sources configured as above

@Bean
public LocalContainerEntityManagerFactoryBean customerEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(customerDataSource())
            .packages(Customer.class)
            .persistenceUnit("customers")
            .build();
}

@Bean
public LocalContainerEntityManagerFactoryBean orderEntityManagerFactory(
        EntityManagerFactoryBuilder builder) {
    return builder
            .dataSource(orderDataSource())
            .packages(Order.class)
            .persistenceUnit("orders")
            .build();
}

The configuration above almost works on its own. To complete the picture you need to configure TransactionManagers for the two EntityManagers as well. One of them could be picked up by the default JpaTransactionManager in Spring Boot if you mark it as @Primary. The other would have to be explicitly injected into a new instance. Or you might be able to use a JTA transaction manager spanning both.

Spring doesn’t require the use of XML to configure the JPA provider, and Spring Boot assumes you want to take advantage of that feature. If you prefer to use persistence.xml then you need to define your own @Bean of type LocalEntityManagerFactoryBean (with id ‘entityManagerFactory’, and set the persistence unit name there.

See JpaBaseConfiguration for the default settings.

Spring Data JPA and Spring Data Mongo can both create Repository implementations for you automatically. If they are both present on the classpath, you might have to do some extra configuration to tell Spring Boot which one (or both) you want to create repositories for you. The most explicit way to do that is to use the standard Spring Data @Enable*Repositories and tell it the location of your Repository interfaces (where ‘*’ is ‘Jpa’ or ‘Mongo’ or both).

There are also flags spring.data.*.repositories.enabled that you can use to switch the auto-configured repositories on and off in external configuration. This is useful for instance in case you want to switch off the Mongo repositories and still use the auto-configured MongoTemplate.

The same obstacle and the same features exist for other auto-configured Spring Data repository types (Elasticsearch, Solr). Just change the names of the annotations and flags respectively.