Spring JPA – Multiple Databases

1. Overview

In this tutorial we’ll implement a simple Spring configuration for a Spring Data JPA system with multiple databases.

2. The Entities

First – let’s create two simple entities – each living in a separate database.

Here is the first entity “User“:

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package org.baeldung.persistence.multiple.model.user;   @Entity @Table (schema = "spring_jpa_user" ) public class User {        @Id      @GeneratedValue (strategy = GenerationType.AUTO)      private int id;        private String name;        @Column (unique = true , nullable = false )      private String email;        private int age; }

And the second entity – “Product“:

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package org.baeldung.persistence.multiple.model.product;   @Entity @Table (schema = "spring_jpa_product" ) public class Product {        @Id      private int id;        private String name;        private double price; }

As you can see, the two entities are also placed in independent packages – this will be important as we move into the configuration.

3. The JPA Repositories

Next – let’s take a look at our two JPA repositories – UserRepository:

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package org.baeldung.persistence.multiple.dao.user;   public interface UserRepository extends JpaRepository<User, Integer> { }

And ProductRepository:

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package org.baeldung.persistence.multiple.dao.product;   public interface ProductRepository extends JpaRepository<Product, Integer> { }

Note, again how we created these two repositories in different packages.

4. Configure JPA with Java

Next – let’s get to the actual Spring configuration. We’ll start by setting up 2 configuration classes – one for the User and the other for the Product.

In each one of this configuration classes, we’ll need to define the following:

• User DataSource
• User EntityManagerFactory (userEntityManager)
• User TransactionManager (userTransactionManager)

Let’s start by looking the the User configuration:

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@Configuration @PropertySource ({ "classpath:persistence-multiple-db.properties" }) @EnableJpaRepositories (      basePackages = "org.baeldung.persistence.multiple.dao.user" ,      entityManagerFactoryRef = "userEntityManager" ,      transactionManagerRef = "userTransactionManager" ) public class UserConfig {      @Autowired      private Environment env;            @Bean      @Primary      public LocalContainerEntityManagerFactoryBean userEntityManager() {          LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();          em.setDataSource(userDataSource());          em.setPackagesToScan( new String[] { "org.baeldung.persistence.multiple.model.user" });            HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();          em.setJpaVendorAdapter(vendorAdapter);          HashMap<String, Object> properties = new HashMap<String, Object>();          properties.put( "hibernate.hbm2ddl.auto" , env.getProperty( "hibernate.hbm2ddl.auto" ));          properties.put( "hibernate.dialect" , env.getProperty( "hibernate.dialect" ));          em.setJpaPropertyMap(properties);            return em;      }        @Primary      @Bean      public DataSource userDataSource() {          DriverManagerDataSource dataSource = new DriverManagerDataSource();          dataSource.setDriverClassName(env.getProperty( "jdbc.driverClassName" ));          dataSource.setUrl(env.getProperty( "user.jdbc.url" ));          dataSource.setUsername(env.getProperty( "jdbc.user" ));          dataSource.setPassword(env.getProperty( "jdbc.pass" ));            return dataSource;      }        @Primary      @Bean      public PlatformTransactionManager userTransactionManager() {          JpaTransactionManager transactionManager = new JpaTransactionManager();          transactionManager.setEntityManagerFactory(userEntityManager().getObject());          return transactionManager;      } }

Notice how we’re using the userTransactionManager as our Primary TransactionManager – by annotating the bean definition with @Primary. That’s helpful whenever we’re going to implicitly or explicitly inject the transaction manager without specifying which one by name.

Next, let’s discuss ProductConfig – where we define similar beans:

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@Configuration @PropertySource ({ "classpath:persistence-multiple-db.properties" }) @EnableJpaRepositories (      basePackages = "org.baeldung.persistence.multiple.dao.product" ,      entityManagerFactoryRef = "productEntityManager" ,      transactionManagerRef = "productTransactionManager" ) public class ProductConfig {      @Autowired      private Environment env;        @Bean      public LocalContainerEntityManagerFactoryBean productEntityManager() {          LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();          em.setDataSource(productDataSource());          em.setPackagesToScan( new String[] { "org.baeldung.persistence.multiple.model.product" });            HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();          em.setJpaVendorAdapter(vendorAdapter);          HashMap<String, Object> properties = new HashMap<String, Object>();          properties.put( "hibernate.hbm2ddl.auto" , env.getProperty( "hibernate.hbm2ddl.auto" ));          properties.put( "hibernate.dialect" , env.getProperty( "hibernate.dialect" ));          em.setJpaPropertyMap(properties);            return em;      }        @Bean      public DataSource productDataSource() {          DriverManagerDataSource dataSource = new DriverManagerDataSource();          dataSource.setDriverClassName(env.getProperty( "jdbc.driverClassName" ));          dataSource.setUrl(env.getProperty( "product.jdbc.url" ));          dataSource.setUsername(env.getProperty( "jdbc.user" ));          dataSource.setPassword(env.getProperty( "jdbc.pass" ));            return dataSource;      }        @Bean      public PlatformTransactionManager productTransactionManager() {          JpaTransactionManager transactionManager = new JpaTransactionManager();          transactionManager.setEntityManagerFactory(productEntityManager().getObject());          return transactionManager;      } }

5. Simple Test

Finally – let’s test our configurations.

We will try a simple test by creating an instance of each entity and make sure it is created – as in the following example:

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@RunWith (SpringJUnit4ClassRunner. class ) @ContextConfiguration (classes = { UserConfig. class , ProductConfig. class }) @TransactionConfiguration public class JPAMultipleDBTest {      @Autowired      private UserRepository userRepository;        @Autowired      private ProductRepository productRepository;        @Test      @Transactional ( "userTransactionManager" )      public void whenCreatingUser_thenCreated() {          User user = new User();          user.setName( "John" );          user.setEmail( "john@test.com" );          user.setAge( 20 );          user = userRepository.save(user);            assertNotNull(userRepository.findOne(user.getId()));      }        @Test      @Transactional ( "userTransactionManager" )      public void whenCreatingUsersWithSameEmail_thenRollback() {          User user1 = new User();          user1.setName( "John" );          user1.setEmail( "john@test.com" );          user1.setAge( 20 );          user1 = userRepository.save(user1);          assertNotNull(userRepository.findOne(user1.getId()));            User user2 = new User();          user2.setName( "Tom" );          user2.setEmail( "john@test.com" );          user2.setAge( 10 );          try {              user2 = userRepository.save(user2);          } catch (DataIntegrityViolationException e) {          }            assertNull(userRepository.findOne(user2.getId()));      }        @Test      @Transactional ( "productTransactionManager" )      public void whenCreatingProduct_thenCreated() {          Product product = new Product();          product.setName( "Book" );          product.setId( 2 );          product.setPrice( 20 );          product = productRepository.save(product);            assertNotNull(productRepository.findOne(product.getId()));      } }

6. Conclusion

This article was a practical overview of how to configure your Spring Data JPA project to use multiple databases.

The full implementation of this article can be found in the github project – this is an Eclipse based project, so it should be easy to import and run as it is.