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Merge does an undesirable persist [message #710278]

Thu, 04 August 2011 21:52

Mauro Flores

Messages: 84
Registered: September 2009
Location: Brasil

Member

The method merge of an entitymanager persist the entity when it doesn't exist.
This can be a problem in a concurrent environment.

An expected updating operation...

1) foo = em.find(foo.id)
2) if (foo != null) // the entity exists!!!
3) em.merge(foo)

can result in an insert, if between lines 2 and 3 the entity foo is deleted by another user.

Can I configure merge to throw an exception when the entity does not exist?

Thanks. Mauro.

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Re: Merge does an undesirable persist [message #710842 is a reply to message #710278]

Fri, 05 August 2011 13:23

Chris Delahunt

Messages: 1389
Registered: July 2009

Senior Member

This is by design to allow attaching new entities to existing object graphs and then merge only the root. The only way to prevent writing of overwriting with stale data is to use optimistic locking (an @Version field) which would throw an exception when a new object already has a lock value.

Best Regards,
Chris

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