Database-aware business objects / listeners

Question

I'm trying to write an EntityListener to apply a numeric edit stamp whenever a business object is inserted or updated. This is pretty trivial in most cases, but I have multiple databases running in the same application (one database per client). I need the edit number to be specific to a client.
Currently my EntityListener methods look something like this:
     @PreUpdate
     void preUpdate(final Auditable auditable) {
          long editNumber = EditNumberGenerator.sharedInstance().nextEditNumber();
          auditable.setEditNumber(editNumber);
          auditable.setModified(new Date());
However, this uses a global EditNumberGenerator. I need this to be district-specific. What I really need is something like this:
     @PreUpdate
     void preUpdate(final Auditable auditable) {
          String databaseName = getEntityManagerParam("databaseName");
          final long editNumber = EditNumberGenerator.getInstance(databaseName).nextEditNumber();
          auditable.setEditNumber(editNumber);
          auditable.setModified(new Date());
     private String getEnityManagerParam(String key) { ... }
I'm not sure I'm explaining this well, but is there some way for my EntityListener (or the business objects themselves) to know what database their EntityManager is pointing to?

Answer 1

If you use a TopLink specific DescriptorEventListener instead of the JPA EventListener you will get a handle on the TopLink session being used and could then query the database or access a database name from the session.
Depending on the edition/version of TopLink you are using you should find information related to this event listener in:
- TopLink Essentials JPA Extensions
- Oracle TopLink 11gR1 (tech preview 3) JPA Extensions
- EclipseLink JPA Extensions
If you need more specifics let me know which TopLink you are using.
Doug