Google App Engine Entity Manager Configuration with Spring 3.0

Question

I'm trying to write a Spring configuration for some basic Google App Engine services. In particular for the EntityManagerFactory and Entity Manager.

To create an EntityManagerFactory from Java code:

EntityManagerFactory emfInstance = javax.persistence.Persistence
    .createEntityManagerFactory("transactions-optional");

Which I would translate as:

<bean id="entityManagerFactory" class="javax.persistence.Persistence" 
    factory-method="createEntityManagerFactory" scope="singleton">
    <constructor-arg value="transactions-optional"/> 
</bean>

And every time I need an EntityManager

EntityManager em = emfInstance.get().createEntityManager(); 

But I don't know how to tell to apply the factory method to the previously created factory.

<bean id="entityManagerProto" 
    factory-method="createEntityManager" scope="prototype"/>

Anyone knows? Thanks.

Answer 1

You can use existing bean as a factory as follows:

<bean id="entityManagerProto"
    factory-bean = "entityManagerFactory"
    factory-method="createEntityManager" scope="prototype"/> 

Also, I'm not sure whether it would work on GAE, but perhaps it would be better to use LocalEntityManagerFactoryBean instead, and get EntityManager injected with @PersistenceContext.