Troubleshooting JPA with Eclipse and Toplink

The error messages provided by JPA demand some interpretation.

Case 1: wrong persistence unit name

make sure that in persistence.xml the persistence-unit name matches what you use in your code, otherwise you get this error:

javax.persistence.PersistenceException: No Persistence provider for EntityManager named GEO_OSB_Persistences:  The following providers:
oracle.toplink.essentials.PersistenceProvider
org.eclipse.persistence.jpa.PersistenceProvider
oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider
Returned null to createEntityManagerFactory.

 at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:154)

Case 2: you did not specify correctly the jta-data-source properties in persistence.xml

SEVERE: Exception in PersistenceManager.getEntityManager: Exception [TOPLINK-4002] (Oracle TopLink Essentials - 2.0 (Build b41-beta2 (03/30/2007))): oracle.toplink.essentials.exceptions.DatabaseException
Internal Exception: java.sql.SQLException: [Microsoft][ODBC Driver Manager] Data source name not found and no default driver specified
Error Code: 0

well, in my case it was because I was using as provider Toplink but the properties were still the Eclipse ones:

eclipselink.jdbc.url instead of toplink.jdbc.url