Multiple Databases with Identical Schemas

[jameswoodward]

Hi,

The company I work for has purchased some automotive industry data from a third party, this comes in the form of two databases, one for Passenger Cars and one for Light Commercial Vehicles. The schemas for the 2 databases are identical.

Currently I have developed Entity beans for the CAR database in a car package and deployed in CAR.JAR. I have had to duplicate (copy-and-paste) these into a lcv package and deployed in LCV.JAR. Each jar has its own persistence.xml that points to the target database.

How can I eliminate this duplication?

How can I access the correct PersistenceContext on-the-fly?

How can I write my Entity beans so that they can be used to query either database, without being deployed in 2 seperate jars?

[eekboom]

Hah - if I understand your problem correctly this is exactly what caused a lot of trial-and-error for me.

After all the only thing I had to do is get my entity manager dynamically rather than having it injected:

public EntityManager getEntityManager(String unit) {
 String path = "java:/EntityManager/" + unit;
 EntityManager entityManager = null;
 try {
 InitialContext context = new InitialContext();
 try {
 entityManager = (EntityManager) context.lookup(path);
 }
 finally {
 context.close();
 }
 }
 catch(NamingException e) {
 LOGGER.log(Level.WARNING, "Cannot retrieve entity manager: " + entityManager, e);
 }

 return entityManager;
 }

where the "unit" parameter is the name of one of the units in your persistence.xmls.

The entity beans don't need any special coding.

This thread discussed the problem a while ago, but I found it more confusing than helpful:
http://jboss.org/index.html?module=bb&op=viewtopic&t=65869&postdays=0&postorder=asc&start=0

What finally got me going was the answer to my own question here:
http://jboss.org/index.html?module=bb&op=viewtopic&t=79597

[jameswoodward]

Many Thanks!

[epbernard]

Actually you cna use @PersistenceContexts or @PersistenceUnits to make this code more portable.