Starting from release with Tapestry 5.3, Tapestry provides a built-in JPA integration which integration with the Java Persistence API (JPA). This module supersedes Tynamo's JPA integration.

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<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             version="2.0">
   <persistence-unit name="DemoUnit"
                     transaction-type="RESOURCE_LOCAL">
       <properties>
          <property name="javax.persistence.jdbc.driver"
                    value="org.h2.Driver" />
          <property name="javax.persistence.jdbc.url"
                    value="jdbc:h2:mem:test" />
          <property name="javax.persistence.jdbc.username"
                    value="sa" />
          <property name="eclipselink.ddl-generation"
                    value="create-tables"/>
          <property name="eclipselink.logging.level"
                    value="fine"/>
      </properties>
   </persistence-unit>

</persistence>

By default, the persistence descriptor persistence descriptor is named persistence.xml and and is expected to be located on the classpath in the META-INF directory.  If If you want to place the the persistence.xml file file in an other another directory or name it arbitrarilydifferently, you can make a contribution to the the SymbolProvider service service, as shown in the following example. This is a quite useful feature if you want to use a different persistence descriptor for tests.

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XML-less JPA configuration

Configuring JPA with With Tapestry, configuring JPA is much more simple simpler than defined as described in the JPA specification. Tapestry allows you to configure the EntityManagerFactory programmatically, without writing any XML configuration files. Imagine you want to use JDBC use JDBC connections managed by the container and provided through JNDI. The resulting persistence descriptor might look like the following one.this:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             version="2.0">
   <persistence-unit name="JTAUnit"
                     transaction-type="RESOURCE_LOCAL">

      <non-jta-data-source>
         jdbc/JPATest
      </non-jta-data-source>

      <properties>
         <property name="eclipselink.ddl-generation"
                   value="create-tables"/>
         <property name="eclipselink.logging.level"
                   value="fine"/>
      </properties>
   </persistence-unit>

</persistence>

Now let's see how to provide the same configuration without to write any single line of XML. The following example demonstrates an demonstrates an equivalent JPA configuration.

public class AppModule {

   @Contribute(EntityManagerSource.class)
   public static void configurePersistenceUnitInfos(MappedConfiguration<String,PersistenceUnitConfigurer> cfg) {

      PersistenceUnitConfigurer configurer = new PersistenceUnitConfigurer() {

         public void configure(TapestryPersistenceUnitInfo unitInfo) {

            unitInfo.nonJtaDataSource("jdbc/JPATest")
               .addProperty("eclipselink.ddl-generation",
                            "create-tables")
               .addProperty("eclipselink.logging.level",
                            "fine");
         }
     };

     cfg.add("JTAUnit", configurer);
   }
}

In the example above you can see a contribution to the EntityManagerSource service. This service is responsible for creating creating the EntityManagerFactory to to be used to create EntityManager. When the service is initialized, it parses the persistence.xml file, if available. For any persistence unit defined in the XML descriptor an a TapestryPersistenceUnitInfo object is created. The The TapestryPersistenceUnitInfo interface is a mutable extension of the the PersistenceUnitInfo interface (defined in the JPA specification) that allows you to configure a persistence unit programmatically.

After parsing the persistence descriptor, the EntityManagerSource service applies its configuration to create further persistence units and/or update the existing ones. The service’s configuration is a map in which persistence unit names are associated with with PersistenceUnitConfigurer instances instances.  A PersistenceUnitConfigurer A PersistenceUnitConfigurer is used to configure a persistence unit programmatically that has been associated been associated with it. In the example above you can see a contribution providing a PersistenceUnitConfigurer for the unit the unit named JTAUnit. 

Automatically adding managed classes classes

If only a single persistence unit is defined, Tapestry scans the  the application-root-package.entities package package. The classes in that package are automatically added as managed classes to the defined persistence unit.

If you have additional packages containing entities, you may contribute them to the the JpaEntityPackageManager service service configuration.

public class AppModule {

   @Contribute(JpaEntityPackageManager.class)
   public static void providePackages(Configuration<String> configuration) {

      configuration.add("org.example.myapp.domain");

      configuration.add("com.acme.model");
   }
}

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The created entity managers can be injected into page, component and other services.  

Injecting the EntityManager into page and component classes

Depending on whether more than one persistence unit has been defined, the way to inject [EntityManager|http://download.oracle.com/javaee/6/api/javax/persistence/EntityManager.html] varies slightly. Let’s inject EntityManager varies slightly. Let’s start with a simple scenario, where only a single persistence unit is defined. In this case, an an EntityManager  can can be injected using the the @Inject  annotationannotation.

public class CreateAddress {

   @Inject
   private EntityManager entityManager;

   @Property
   private Address address;

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

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

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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 the @PersistenceContext  annotation’ s annotation’s name attribute attribute is used for?  The The following example demonstrates how to inject the persistence unit named DemoUnit.  

public class CreateAddress {

   @PersistenceContext(unitName = "DemoUnit")
   private EntityManager entityManager;

   @Property
   private Address address;

   @CommitAfter
   @PersistenceContext(unitName = "DemoUnit")
   void onSuccess() {
      entityManager.persist(address);
   }
}

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While component injection occurs only on fields, the injection in the IoC layer may be triggered by a  a field or a constructor. The following example demonstrates field injection, when a single persistence unit is defined in the persistence descriptor.

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If multiple persistence units are defined in the same application, you need to disambiguate the unit to inject. This is done by placing the @PersistenceContext annotationwith the @PersistenceContext annotation, as shown in the following example.  Because Because @PersistenceContext  annotation must not be placed on constructor parameters, you can’t use constructor injection and must switch to field injection.

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Transaction management

As you may already know from the Hibernate integration library, Tapestry automatically manages transactions for you. The JPA integration library defines the @CommitAfter _the @CommitAfter annotation, which acts as the correspondent annotation from the Hibernate integration library. Let’s explore the _the UserDAO interface interface to see the annotation in action.

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As you can see, the annotation may be placed on service method in order to mark that method as transactional. Any method marked with with the @CommitAfter  annotation annotation will have a transaction started before, and committed after, it is called. Runtime exceptions thrown by by a transactional method will abort the transaction. Checked exceptions are ignored and the transaction will be committed anyway.

After placing the the @CommitAfter  annotation annotation on methods, you need to tell Tapestry to advise those methods. This is accomplished by adding the transaction advice, as shown in the following example.

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