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Depending on whether more than one persistence unit has been defined, the way to inject EntityManager varies slightly. Let’s start with a simple scenario, where only a single persistence unit is defined. In this case, an EntityManager can be injected using the @Inject @PersistenceContext annotation.

public class CreateAddress {

   @Inject@PersistenceContext
   private EntityManager entityManager;

   @Property
   private Address address;

   @CommitAfter
   void onSuccess() {
      entityManager.persist(address);
   }
}

Alternatively, you can use the @PersistenceContext @Inject annotation to get the EntityManager injected into a page or component, as shown in the following example.

public class CreateAddress {

   @PersistenceContext@Inject
   private EntityManager entityManager;

   @Property
   private Address address;

   @CommitAfter
   void onSuccess() {
      entityManager.persist(address);
   }
}

If However, if you have multiple instances of persistence-unit defined in the same application, you need to explicitly tell Tapestry which persistence unit you want to get injected. This is what the @PersistenceContext annotation’s name attribute is used for? The following example demonstrates how to inject the persistence unit named DemoUnit.

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