3 Replies Latest reply on Jun 10, 2007 9:36 AM by alrubinger

difference between @Version and EntityManager.lock

adamzrk Jun 9, 2007 11:36 AM

Hi

What is the difference between @Version and EntityManager.lock method?
When I use @version then If one client is updating entity the version attribute is being increased and if another client wants to update the same entity the OptimisticLockException is thrown - there is no wainting for the second client?
What is the situation with the lock method?

Regards
Adam

1. Re: difference between @Version and EntityManager.lock

waynebaylor Jun 9, 2007 8:38 PM (in response to adamzrk)

The OptimisticLockException indicates that the second client has a stale version of the entity, i.e. it won't be updating the latest version.

As far as I know, using the EntityManager.lock method will force the version to be incremented, whether or not you actually changed the entity.
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2. Re: difference between @Version and EntityManager.lock

adamzrk Jun 10, 2007 6:03 AM (in response to adamzrk)

So, i guess, when using only version without lock there won't be increment of version attribute? Is it possible? I thought that version is always incremented after update.
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3. Re: difference between @Version and EntityManager.lock

alrubinger Jun 10, 2007 9:36 AM (in response to adamzrk)

@Version will enable JPA Optmistic locking for the entity. EM.lock allows the application to specify the lock mode to be used on the versioned object.

http://java.sun.com/javaee/5/docs/api/javax/persistence/LockModeType.html

This is no JPA "waiting" or caching of updates to an entity until another Tx is finished with it; that responsibility is on the part of the application. JPA locking provides you with a mechinism to ensure your data integrity is kept.

S,
ALR
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