Java EE (Java Enterprise Edition) General Discussion

Hello, I'm looking for the persistence in EJB

	@PersistenceContext(name = "postgres")
	private EntityManager em;

persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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">
  <persistence-unit name="postgres" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <exclude-unlisted-classes>false</exclude-unlisted-classes>
    <properties>
      <property name="eclipselink.target-database" value="PostgreSQL"/>
      <property name="eclipselink.logging.level" value="INFO"/>
      <property name="eclipselink.jdbc.driver" value="org.postgresql.Driver"/>
      <property name="eclipselink.jdbc.url" value="jdbc:postgresql://localhost:5432/thunor"/>
      <property name="eclipselink.jdbc.password" value="heslo"/>
      <property name="eclipselink.jdbc.user" value="persistence"/>
    </properties>
  </persistence-unit>
</persistence

but when I try to run the project, I'l get following errors:

java.lang.RuntimeException: Could not resolve a persistence unit corresponding to the persistence-context-ref-name [postgres] in the scope of the module called [Thunor]. Please verify your application.

the passwords and user works when calling from terminal

coub /tmp  $ psql -U persistence thunor
Password for user persistence: *****
psql (8.4.2)
Type "help" for help.

thunor=> \q
coub /tmp  $

I've googled through entire internet, and there isn't satisfying (problem solving answer).
Do anybody know where is the problem?
Thanks for answering.