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26.6. Using a Seam-Managed Persistence Context in Spring

Some of Seam's most powerful features are its conversation scope, and the ability to keep an EntityManager open for the life of a conversation. These eliminate many problems associated with detaching and reattaching entities, and mitigate the occurrence of LazyInitializationException. Spring does not provide a way to manage persistence contexts beyond the scope of a single web request (OpenEntityManagerInViewFilter).
Seam brings conversation-scoped persistence context capabilities to Spring applications by allowing Spring developers to access a Seam-managed persistence context with the JPA tools provided with Spring (PersistenceAnnotationBeanPostProcessor, JpaTemplate, etc.)
This integration work provides:
  • transparent access to a Seam-managed persistence context using Spring-provided tools
  • access to Seam conversation-scoped persistence contexts in a non-web request — for example, an asynchronous Quartz job
  • the ability to use Seam-managed persistence contexts with Spring-managed transactions. This requires manual flushing of the persistenct context.
Spring's persistence context propagation model allows only one open EntityManager per EntityManagerFactory, so the Seam integration works by wrapping an EntityManagerFactory around a Seam-managed persistence context, like so: 
<bean id="seamEntityManagerFactory" 
    class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean"> 
  <property name="persistenceContextName" value="entityManager"/> 
</bean>
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Here, persistenceContextName is the name of the Seam-managed persistence context component. By default, this EntityManagerFactory has a unitName equal to the Seam component name — in this case, entityManager. If you wish to provide a different unitName, you can provide a persistenceUnitName like so: 
<bean id="seamEntityManagerFactory" 
    class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean">
  <property name="persistenceContextName" value="entityManager"/>
  <property name="persistenceUnitName" value="bookingDatabase:extended"/>
</bean>
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This EntityManagerFactory can now be used in any Spring-provided tools; in this case, you can use Spring's PersistenceAnnotationBeanPostProcessor just as you would in Spring. 
<bean class="org.springframework.orm.jpa.support
             .PersistenceAnnotationBeanPostProcessor"/>
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If you define your real EntityManagerFactory in Spring, but wish to use a Seam-managed persistence context, you can tell the PersistenceAnnotationBeanPostProcessor your desired default persistenctUnitName by specifying the defaultPersistenceUnitName property.
The applicationContext.xml might look like: 
<bean id="entityManagerFactory" 
      class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean">
  <property name="persistenceUnitName" value="bookingDatabase"/>
</bean>
<bean id="seamEntityManagerFactory" 
    class="org.jboss.seam.ioc.spring.SeamManagedEntityManagerFactoryBean">
  <property name="persistenceContextName" value="entityManager"/>
  <property name="persistenceUnitName" value="bookingDatabase:extended"/>
</bean>
<bean class="org.springframework.orm.jpa
             .support.PersistenceAnnotationBeanPostProcessor">
  <property name="defaultPersistenceUnitName" 
            value="bookingDatabase:extended"/>
</bean>
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The component.xml might look like: 
<persistence:managed-persistence-context name="entityManager" 
    auto-create="true" entity-manager-factory="#{entityManagerFactory}"/>
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JpaTemplate and JpaDaoSupport have an identical configuration in a Spring-based persistence context and in a normal Seam-managed persistence context. 
<bean id="bookingService" 
      class="org.jboss.seam.example.spring.BookingService"> 
  <property name="entityManagerFactory" ref="seamEntityManagerFactory"/> 
</bean>
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