How to use a second data source in spring? - spring-boot

Question

I downloaded the example code here
https://github.com/spring-projects/spring-data-examples/tree/master/jpa/multiple-datasources
but I still don't understand how an repository is connected to a datasource. Even when I look into the config class, it makes no reference to a repository. And inside the repository interface it makes no reference to the data source or config.
So when you use two different repositories to save, how does it know which datasource to go to for each repo?

Answer 1

In the repository with examples you linked, each config class is annotated with #EnableJpaRepositories that does scanning for repositories only in the package of annotated class plus subpackages - this is where the relation between datasource and repository happens.

Answer 2

Notice the configurations (commented as /* important */)
in OrderConfig
#Configuration
/* important */
#EnableJpaRepositories(entityManagerFactoryRef = "orderEntityManagerFactory",
transactionManagerRef = "orderTransactionManager")
class OrderConfig {
#Bean
PlatformTransactionManager orderTransactionManager() {
return new JpaTransactionManager(orderEntityManagerFactory().getObject());
}
#Bean
LocalContainerEntityManagerFactoryBean orderEntityManagerFactory() {
HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
vendorAdapter.setGenerateDdl(true);
LocalContainerEntityManagerFactoryBean factoryBean = new LocalContainerEntityManagerFactoryBean();
/* important */
factoryBean.setDataSource(orderDataSource());
factoryBean.setJpaVendorAdapter(vendorAdapter);
factoryBean.setPackagesToScan(OrderConfig.class.getPackage().getName());
return factoryBean;
}
#Bean
DataSource orderDataSource() {
return new EmbeddedDatabaseBuilder().//
setType(EmbeddedDatabaseType.HSQL).//
setName("orders").//
build();
}
}
and, CustomerConfig
#Configuration
/* important */
#EnableJpaRepositories(entityManagerFactoryRef = "customerEntityManagerFactory",
transactionManagerRef = "customerTransactionManager")
class CustomerConfig {
#Bean
PlatformTransactionManager customerTransactionManager() {
return new JpaTransactionManager(customerEntityManagerFactory().getObject());
}
#Bean
LocalContainerEntityManagerFactoryBean customerEntityManagerFactory() {
HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter();
jpaVendorAdapter.setGenerateDdl(true);
LocalContainerEntityManagerFactoryBean factoryBean = new LocalContainerEntityManagerFactoryBean();
/* important */
factoryBean.setDataSource(customerDataSource());
factoryBean.setJpaVendorAdapter(jpaVendorAdapter);
factoryBean.setPackagesToScan(CustomerConfig.class.getPackage().getName());
return factoryBean;
}
#Bean
DataSource customerDataSource() {
return new EmbeddedDatabaseBuilder().//
setType(EmbeddedDatabaseType.HSQL).//
setName("customers").//
build();
}
}
and, finally the #Transactional annotation in DataInitializer
/* important */
#Transactional("customerTransactionManager")
public CustomerId initializeCustomer() {
return customers.save(new Customer("Dave", "Matthews")).getId();
}
uses customerTransactionManager which is configured in CustomerConfig
and,
/* important */
#Transactional("orderTransactionManager")
public Order initializeOrder(CustomerId customer) {
Assert.notNull(customer, "Customer identifier must not be null!");
Order order = new Order(customer);
order.add(new LineItem("Lakewood Guitar"));
return orders.save(order);
}
uses orderTransactionManager which is configured in OrderConfig
Basically, you're configuring different datasources, different entityManagers, different transactionManagers and refer to them specifically as per your choice.