How to configure transaction management for working with 2 different db in Spring?

Question

I have 2 databases (MySql and HSQLDB). I configured 2 data sources and 2 EntityManagerFactory beans. I can also configure 2 correspondent JpaTransactionManager beans.

But I don't know how to specify which of them should be used to manage transactions for concrete service-class. I want to use @Transactional annotation for that purpose, but I actually can specify only one of txManagers:

<tx:annotation-driven transaction-manager="manager"/>

What is the way out from this situation?

Answer 1

Declare your <tx:annotation-driven> without transaction-manager attribute, declare qualifiers for transaction managers like this:

<bean id="jpaTransactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
 <property name="entityManagerFactory" ref="entityManagerFactory" />
 <qualifier value="txManager1"/>
</bean>

Use this qualifier in @Transactional as a value to select one of transaction managers:

@Transactional("txManager1")

or, with more properties:

@Transactional(value = "txManager1", readOnly = true)

Answer 2

The javadoc for JpaTransactionManager has some advice on this:

This transaction manager is appropriate for applications that use a single JPA EntityManagerFactory for transactional data access. JTA (usually through JtaTransactionManager) is necessary for accessing multiple transactional resources within the same transaction. Note that you need to configure your JPA provider accordingly in order to make it participate in JTA transactions.

In other words, if you find yourself with multiple entity managers, with corresponding tx managers, then you should consider using a single JtaTransactionManager instead. The entity managers should be able to participate in JTA transactions, and this will give you full transactionality across both entity managers, without hacving to worry about which entity manager you're in at any one time.

Of course, JtaTransactionManager does require a full JTA-supporting application server, rather than a vanilla servlet engine like Tomcat.