Sample EntityManager usage in Java and Python WLST

In Eclipse, create a JDBC Connection
show view Data Source Explorer
new Connection Profile (enter parameters for your schema)

New JPA project
JPA Tools, Generate Entities from Tables

you should have a persistence.xml which contains

<?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="ToplinkTest" transaction-type="RESOURCE_LOCAL">
  <class>com.osb.reporting.WliQsReportAttribute</class>
  <class>com.osb.reporting.WliQsReportData</class>
  <properties>
   <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@localhost:1521:xe"/>
   <property name="javax.persistence.jdbc.user" value="DEV_SOAINFRA"/>
   <property name="javax.persistence.jdbc.password" value="DEV_SOAINFRA"/>
   <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
  </properties>
 </persistence-unit>
</persistence>

You can now code the client:

package com.osb.reporting.client;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

import com.osb.reporting.WliQsReportAttribute;

public class ReportingClient {
 public static void main(String[] args) throws ClassNotFoundException {
  EntityManagerFactory emf = Persistence.createEntityManagerFactory("ToplinkTest");
  EntityManager em = emf.createEntityManager();
  WliQsReportAttribute result = em.find(WliQsReportAttribute.class, "uuid:0e6fb58fc7c49289:5378b92d:134416bc5f5:-7fbe");
  System.out.println(result.getMsgLabels());
  Query fa = em.createQuery("select a from WliQsReportAttribute a");
  List res = fa.getResultList();
  for (Object el : res) {
   System.out.println( ((WliQsReportAttribute)el).getMsgLabels());
  }
 }
}

you will need to add the JDBC driver to the classpath, like
C:\bea1035\wlserver_10.3\server\ext\jdbc\oracle\11g\ojdbc5_g.jar

In WLST, just add to the classpath the location from which you can access classes and META-INF (where persistence.xml is located).... like the build\classes directory.

package com.osb.reporting.client;

from javax.persistence import *
emf = Persistence.createEntityManagerFactory("CMBDModeling")
em = emf.createEntityManager()
q = em.createQuery("select envs from Nesoa2Env envs")
res = q.getResultList()
for i in res:
   print i.envname

so the message is: you can easily use JPA in WLST and get rid of all that horrible pain of reading property files, by accessing directly a DB

To Merge or To Persist....

http://download.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#merge%28T%29

Merge the state of the given entity into the current persistence context.


more info here (from the JPA 1.0 specs)

Hibernate has this to say.


if you entityManager.persist(anEntity), and they you entityManager.persist(anEntity) again, you will get a UNIQUE_KEY contraint violation (it will save it twice with the same ID)



in doubt, just use merge and you will be safe:
if you invoke it with a unpersisted entity it will do an INSERT
if you invoke it with an already persisted entity it will do an UPDATE

EntityManager must be access within a transaction

The error means of course
"EntityManager must be accessED within a transaction"

annotating your EJB method with:
@TransactionAttribute(TransactionAttributeType.REQUIRED)

(which is the default), ensures that
"If the client is not associated with a transaction, the container starts a new transaction before running the method."

(see here)
( see also discussion here)

Using the
em.joinTransaction();


you can annotate your method with
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
to make sure you join a brand new transaction