Question

When creating new entities from user input I can’t be sure that there is no other entity with identical data. The only examples I was able to find used predefined Ids, so one could check if the entity exists by calling entityManager.find(id). If the id is generated, I see several ways to persist safely:

• call entityManager.persist and hope for the best – catching the EntityExistsException and either swallowing it or displaying an error message
• call entityManager.merge and let JPA do the checking…will it always work properly?
• search for the entity by a query – jPQL or criteria and call entityManager.persist if not found

My intuition is to go with the third approach, but is there a better way still?

I am working with JPA 2 and would like to avoid vendor-specific solutions (like Hibernate’sSessionManager.saveOrUpdate)

Answer 1

If you really can’t predict whether the newly generated ID will be unique I’d definitely go with the third approach.

Also, I don’t think you’ll need Criteria for such a simple query, and in most cases the cost of that extra query won’t be very costly.