Hibernate.orgCommunity Documentation
This tutorial is located within the download bundle under entitymanager and illustrates
using annotations to provide mapping information
using JPA
The previous tutorials used the Hibernate-specific
hibernate.cfg.xmlpersistence.xml. How this bootstrapping works is defined
by the JPA specification. In Java™ SE environments the
persistence provider (Hibernate in this case) is required to locate all JPA
configuration files by classpath lookup of the META-INF/persistence.xml resource
name.
Example 4.1. persistence.xml
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="org.hibernate.tutorial.jpa">
...
</persistence-unit>
</persistence>
persistence.xml files should provide a unique name for each
persistence unit. This name is how applications reference the configuration
while obtaining an javax.persistence.EntityManagerFactory reference.
The settings defined in the properties element were already discussed in
Section 2.1, “The Hibernate configuration file”. Here the javax.persistence-prefixed
varieties are used when possible. For the remaining Hibernate-specific configuration setting names notice
that they are now prefixed with hibernate..
Additionally, the class element functions the same as discussed in
Section 3.1, “The Hibernate configuration file”.
The entity is exactly the same as that from the annotations tutorial. See Section 3.2, “The annotated entity Java class”
The previous tutorials used the Hibernate APIs. This tutorial uses the JPA APIs.
Example 4.2. Obtaining the javax.persistence.EntityManagerFactory
protected void setUp() throws Exception {
entityManagerFactory = Persistence.createEntityManagerFactory( "org.hibernate.tutorial.jpa" );
}
Notice again the use of org.hibernate.tutorial.jpa as the
persistence unit name, which matches from Example 4.1, “persistence.xml”
Example 4.3. Saving (persisting) entities
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
entityManager.persist( new Event( "Our very first event!", new Date() ) );
entityManager.persist( new Event( "A follow up event", new Date() ) );
entityManager.getTransaction().commit();
entityManager.close();
The code is pretty similar to Example 2.5, “Saving entities”. Here
we use an javax.persistence.EntityManager as opposed to a
org.hibernate.Session. JPA calls this operation
persist instead of save.
Example 4.4. Obtaining a list of entities
entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
List<Event> result = entityManager.createQuery( "from Event", Event.class ).getResultList();
for ( Event event : result ) {
System.out.println( "Event (" + event.getDate() + ") : " + event.getTitle() );
}
entityManager.getTransaction().commit();
entityManager.close();
Again, the code is pretty similar to Example 2.6, “Obtaining a list of entities”.
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