multiple entitymanagers in a transaction

Question

I am writing an application that will move data from one database to another Using JPA EntityManager API. My questions are : 1. Can i use multiple entity managers in a single transaction? 2. Can i read an entity from one database and persist it in the other? what are the issues that am likely to encounter?

Answer 1

Can I use multiple entity managers in a single transaction?

Yes, using JTA. I'm not sure you need a global transaction in your case though. Are you really moving or copying entities from one DB to the other? In the later case, you could use two transactions sequentially.

Can I read an entity from one database and persist it in the other?

Assuming they have the same structure and you don't have any conflicting PK, it should be possible to read an entity using a first entity manager, detach it and then merge it using another entity manager. If you have possible PK conflicts, you'll have to use a DIY approach (vs a simple merge).