docs/persistence-context.adoc

= persistence-context
:index-group: JPA
:jbake-date: 2018-12-05
:jbake-type: page
:jbake-status: published

= Via annotation

Both lookup and injection of an EntityManager can be configured via the
`@PersistenceContext` annotation.

[source,java]
----
package org.superbiz;

import javax.persistence.PersistenceContext;
import javax.persistence.EntityManager;
import javax.ejb.Stateless;
import javax.naming.InitialContext;

@Stateless
@PersistenceContext(name = "myFooEntityManager", unitName = "foo-unit")
public class MyBean implements MyInterface {

    @PersistenceContext(unitName = "bar-unit")
    private EntityManager myBarEntityManager;

    public void someBusinessMethod() throws Exception {
        if (myBarEntityManager == null) throw new NullPointerException("myBarEntityManager not injected");

        // Both can be looked up from JNDI as well
        InitialContext context = new InitialContext();
        EntityManager fooEntityManager = (EntityManager) context.lookup("java:comp/env/myFooEntityManager");
        EntityManager barEntityManager = (EntityManager) context.lookup("java:comp/env/org.superbiz.MyBean/myBarEntityManager");
    }
}
----

= Via xml

The above `@PersistenceContext` annotation usage is 100% equivalent to the
following xml.

[source,xml]
----
<persistence-context-ref>
    <persistence-context-ref-name>myFooEntityManager</persistence-context-ref-name>
    <persistence-unit-name>foo-unit</persistence-unit-name>
    <persistence-context-type>Transaction</persistence-context-type>
</persistence-context-ref>

<persistence-context-ref>
    <persistence-context-ref-name>org.superbiz.calculator.MyBean/myBarEntityManager</persistence-context-ref-name>
    <persistence-unit-name>bar-unit</persistence-unit-name>
    <persistence-context-type>Transaction</persistence-context-type>
    <injection-target>
        <injection-target-class>org.superbiz.calculator.MyBean</injection-target-class>
        <injection-target-name>myBarEntityManager</injection-target-name>
    </injection-target>
</persistence-context-ref>
----