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[{ALLOW edit Authenticated}]
!JPA - Java Persitence API
|Download API|[http://mirrors.ibiblio.org/pub/mirrors/maven2/javax/persistence/persistence-api/1.0/]
Special topic: [Mapping a many-to-many join table with extra column using JPA with EclipseLink|JPA_ManyToMany]
* Defines a common set of functionality for ORM (object relation mapping)
* Uses Annotations (Since Java 5.0) or XML mappings
* You need a "Persistence Provider", because the JPA contains just the rules
* Providers are (you can use any)
** EclipseLink, former [TopLink|http://www.oracle.com/technology/products/ias/toplink/jpa/index.html] (comes with glassfish)
** Hibernate (comes with JBoss)
** [OpenJPA|http://openjpa.apache.org/] (comes with Geronimo)
* [JPQL reference|http://download.oracle.com/docs/cd/E11035_01/kodo41/full/html/ejb3_langref.html]
!Use JPA and EclipseLink on Java SE (Standalone, without Container or AppServer)
(see also [here|http://www.zdnet.de/anwendungsentwicklung_ejb_persistenz_mit_java_se_story-20000201-39142744-1.htm]
and [here|http://www.redhat.com/docs/manuals/jboss/jboss-eap-4.2/doc/hibernate/Entity_Manager_User_Guide/Setup_and_configuration-Obtaining_an_EntityManager_in_a_Java_SE_environment.html]
and this [example|http://javahowto.blogspot.com/2006/07/helloworld-with-jpa-toplink-and-mysql.html])
1. Create a folder "meta-inf" under your src and create the file "persistence.xml" with all information for
the EntityManagerFactory (provider) to create an instance of EntityManager:
{{{
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0"
xmlns="http://java.sun.com/xml/ns/persistence">
<persistence-unit name="dp">
<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
<class>ebel.auth.User</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
<properties>
<property name="eclipselink.logging.level" value="FINE" />
<property name="eclipselink.logging.thread" value="true" />
<property name="eclipselink.logging.session" value="true" />
<property name="eclipselink.logging.timestamp" value="true" />
<property name="eclipselink.logging.exceptions" value="true" />
<property name="eclipselink.jdbc.url" value="jdbc:mysql://localhost:3306/databasename" />
<property name="eclipselink.jdbc.user" value="root" />
<property name="eclipselink.jdbc.password" value="xxx" />
<property name="eclipselink.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="eclipselink.jdbc.read-connections.min"
value="1" />
<property name="eclipselink.jdbc.write-connections.min"
value="1" />
<!-- <property name="eclipselink.ddl-generation" value="create-tables" />
-->
</properties>
</persistence-unit>
</persistence>
}}}
You can lookup settings here:
|EntityManagerFactory Properties|[http://wiki.eclipse.org/EclipseLink/Features/JPA#EntityManagerFactory_Properties]
|EclipseLink Specific Settings (Properties)|[http://wiki.eclipse.org/Using_EclipseLink_JPA_Extensions_%28ELUG%29]
|Annotations|[http://www.oracle.com/technology/products/ias/toplink/jpa/resources/toplink-jpa-annotations.html#IndexOfAnnotations]
2. Get the libs \\
(you can download glassfish and copy the jars)
{{{
JDBC-Driver
my-sql-connector-java-5.1.7-bin.jar (or any other jdbc driver)
EclipseLink
org.eclipse.persistence.antlr.jar
org.eclipse.persistence.asm.jar
org.eclipse.persistence.core.jar
org.eclipse.persistence.jpa.jar
JPA
javax.persistence.jar
}}}
3. Get an Entity Manager
{{{
emf = Persistence.createEntityManagerFactory("dp");
em = emf.createEntityManager();
...
em.close();
emf.close()
}}}
__Note1: You should encapsulate the creation of the Entity Manager in a Singleton Pattern, e.g. make sure you use and reuse only one instance of it. Otherwise you get the whole initialization for each instantiation. Especially if you use
<property name="eclipselink.ddl-generation" value="drop-and-create-tables" />
all tables will be dropped and recreated each time you instantiate the entity manager.__
4. Use it (for example save object User)
{{{
em.getTransaction().begin();
User u = new User("hugo", "password");
em.persist(u);
em.getTransaction().commit();
}}}
! Use JPA with Dependency Injection
* This works only with EJBs
* It is not sufficient to annotate a class only !
* You need to let the AppServer give you an EJB, e.g. request one instance from JNDI
* the app server should tell you the JNDI name of the EJB during boot in the log
* see also [here|http://weblogs.java.net/blog/ss141213/archive/2005/12/using_java_pers.html]
5. [JPA OneToMany not deleting child|http://stackoverflow.com/questions/2011519/jpa-onetomany-not-deleting-child], use following provider additions:\\
|EclipseLink|@PrivateOwned
|Hibernate|{{{@Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE,
org.hibernate.annotations.CascadeType.DELETE,
org.hibernate.annotations.CascadeType.MERGE,
org.hibernate.annotations.CascadeType.PERSIST,
org.hibernate.annotations.CascadeType.DELETE_ORPHAN})
}}}
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