jpa 2.0 - Perform UPDATE without SELECT in eclipselink

Question

Is is possible (without writing custom SQL) to have Eclipselink trust me as to whether to perform an update or insert on a merge, rather than perform a select, then an update or insert? If so, how?

In my mind I'd like to use a transient flag and a custom if statement to determine whether the item is already in the database or not, and instruct eclipselink to perform the query required. I understand Hibernate provides this as update() and save()

A few notable points:

• I have a large amount of objects that are being batch-merged, as such persist() is not suitable for me (also the objects do not exist in the library except when they are passed in for the merge anyway)
• Because there are so many objects being merged, it is unlikely that there will be any cache hits, so eclipselink has been unable to tell if its sent it in before via the cache
• Because amount of objects going in (to a non-local database, in this case) the SELECTs are a problem, especially given I can tell which will be required before the operation occurs
• I'd really rather not switch to Hibernate

Thanks. Perhaps I am missing something obvious!

Answer 1

What you are looking for is called existence checking in EclipseLink, and can be configured using the @ExistenceChecking annotation as described here: http://eclipse.org/eclipselink/documentation/2.4/jpa/extensions/a_existencechecking.htm

Try specifying @ExistenceChecking(ExistenceType.CHECK_CACHE) as while it states that check_cache is the default,this is for Native EclipseLink projects. JPA projects use a Check_Database as the default to conform to the JPA specification requiring that merge calls merge into data from the database if necessary. Using the check_cache will prevent EclipseLink from querying at all, so you can query yourself based on your own criteria. Existing objects will be required to be in the cache though, otherwise there is nothing to merge into, and EclipseLink will have to perform an insert.

Another option is to use a customizer to define the DoesExistQuery used for each class. This could allow you to override the checkEarlyReturn method to perform as needed to determine existence.

The above options still use the JPA merge and so still require getting the existing data to merge into - so it will still require selects for existing objects not in the cache. If all you are after is an update all type statement that will update the object or insert the object as is, without tracking only what has changed, you might try looking at native EclipseLink functionality, such as the UnitOfWork api. Using something like ((EntityManagerImpl)em.getDelegate()).getUnitOfWork().updateObject(entity) or use the UOW execute your own UpdateObjectQuery would avoid the selects for existing objects, at the loss of only sending changes.