Migrating from Hibernate to JPA

From Foochal

Contents 1 Move from SessionFactory creation to entity manager factory using 1.1 Spring migration of SessionFactory, if needed 1.2 Migrating java code 2 Migrate hibernate.cfg.xml to persistence.xml

Move from SessionFactory creation to entity manager factory using

Ejb3Configuration cfg = new Ejb3Configuration();
EntityManagerFactory emf = cfg.configure("/mypath/hibernate.cfg.xml")
                             .buildEntityManagerFactory(); //Create the entity manager factory

Spring migration of SessionFactory, if needed

Original:

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
 <property name="dataSource">
  <ref bean="dataSource" />
 </property>
 <property name="configurationClass">
  <value>org.hibernate.cfg.AnnotationConfiguration</value>
 </property>
 <property name="configLocation">
  <value>classpath:hibernate.cfg.xml</value>
 </property>
</bean>

Migrating java code

Old	New
SessionFactory.openSession()	EntityManagerFactory.createEntityManager()
Session.getNamedQuery()	EntityManager.createNameQuery()
Query.list()	Query.getResultList()
Query.setString()	Query.setParameter()
Query.uniqueResult()	Query.getSingleResult()
Session.saveOrUpdate()	EntityManager.persist()
Query.setParameterList()	Query.setParameter()
Session.createCriteria()	EntityManager.createQuery()
Session.createSQLQuery()	Session.createNativeQuery()
Session.update()	EntityManager.merge()
Session.saveOrUpdate() http://forum.springframework.org/showthread.php?t=36064 copies the newly managed persistent state onto the object passed	EntityManager.merge() does not copy the newly managed persistent state onto the object passed. http://www.hibernate.org/hib_docs/entitymanager/reference/en/html_single/#d0e658 http://www.hibernate.org/hib_docs/entitymanager/reference/en/html_single/#d0e880 The merge operation is clever enough to automatically detect whether the merging of the detached instance has to result in an insert or update.

Migrate hibernate.cfg.xml to persistence.xml

The mapping from hibernate.cfg.xml to persistence.xml is pretty straightforward, here's a sample persistence.xml

<?xml version='1.0' encoding='utf-8'?>
<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_1_0.xsd"
  version="1.0">
 <persistence-unit name="manager1">
  <provider>org.hibernate.ejb.HibernatePersistence</provider>
  <jta-data-source>java:comp/env/jdbc/MyDataSource</jta-data-source>
  <class>
    org.foochal.Employee
  </class>
 </persistence-unit>
</persistence>

You need to put your persistence.xml where it can be looked up by the classpath resource name:

META-INF/persistence.xml

I had to put it in

WEB-INF/classes/META-INF/persistence.xml

..and only then the classloader was able to pick it up