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10.3. Seam-managed persistence contexts

If you use Seam outside a Java EE 5 environment, you cannot rely upon the container to manage the persistence context lifestyle. Even within EE 5 environments, propagating the persistence context between loosely-coupled components in a complex application can be difficult and error-prone.
In this case, you will need to use a managed persistence context (for JPA) or a managed session (for Hibernate) in your components. A Seam-managed persistence context is just a built-in Seam component that manages an instance of EntityManager or Session in the conversation context. You can inject it with @In.
Seam-managed persistence contexts are extremely efficient in a clustered environment. Seam can perform optimizations for container-managed persistence contexts that the EJB3 specification does not allow. Seam supports transparent failover of extended persistence contexts, without replicating any persistence context state between nodes. (We hope to add this support to the next revision of the EJB specification.)

10.3.1. Using a Seam-managed persistence context with JPA
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Configuring a managed persistence context is easy. In components.xml, write: 
<persistence:managed-persistence-context name="bookingDatabase" 
   auto-create="true" 
   persistence-unit-jndi-name="java:/EntityManagerFactories/bookingData"/>
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This configuration creates a conversation-scoped Seam component named bookingDatabase, which manages the life cycle of EntityManager instances for the persistence unit (EntityManagerFactory instance) with JNDI name java:/EntityManagerFactories/bookingData.
You must bind the EntityManagerFactory into JNDI. In JBoss, you can do this by adding the following property setting to persistence.xml. 
<property name="jboss.entity.manager.factory.jndi.name" 
          value="java:/EntityManagerFactories/bookingData"/>
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Now we can inject our EntityManager with: 
@In EntityManager bookingDatabase;
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If you use EJB3, and mark your class or method @TransactionAttribute(REQUIRES_NEW), then the transaction and persistence context should not propagate to method calls on this object. However, since the Seam-managed persistence context propagates to any component within the conversation, it propagates to methods marked REQUIRES_NEW. Therefore, if you mark a method REQUIRES_NEW, you should access the entity manager with @PersistenceContext.
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