Hi, all. I am hoping you can help me out here. You don't have a users list so I'm sending it to dev.

I've been implementing some code against JPA and I was trying to figure out how to handle a transaction rollback. I wasn't sure if JPA is responsible for rolling back the state of any objects in the persistence context.

The answer appears to be no, and I found this in the spec:

3.3.2 Transaction Rollback

For both transaction-scoped and extended persistence contexts, transaction rollback causes all pre-existing managed instances and removed instances[15] to become detached. The instances’ state will be the state of the instances at the point at which the transaction was rolled back. Transaction rollback typically causes the persistence context to be in an inconsistent state at the point of rollback. In particular, the state of version attributes and generated state (e.g., generated primary keys) may be inconsistent. Instances that were formerly managed by the persistence context (including new instances that were made persistent in that transaction) may therefore not be reusable in the same manner as other detached objects—for example, they may fail when passed to the merge operation.

As an app writer, this statement is somewhat disconcerting.

I was wondering if there is any guidance available for how I can write an app against JPA that handles rollback correctly.

I'm writing a controller that interacts with entity objects, passing them around to various methods, storing them in member variables, and so on. I don't want to detach them, because (a) it is costly for me to copy all the data into a separate, detached instance, and then during the merge operation to have them copied back into the instance stored in the persistence context and (b) I never know if I can access a field or relationship because I don't know if the field or related instance has been loaded yet. When I keep them attached, JPA takes care of this for me.

Then let's say I perform a persist() operation and it fails and rolls back. This means all my objects I've been passing around and storing in various places are suddenly detached and "may be" in an inconsistent state (which from the perspective of a program is the same as saying they *are* in an inconsistent state), and thus are invalid.

So now what do I do? Is there a recommended approach for dealing with this? How does my application detect this in some global way, and reloads from the persistence context all the instances it was keeping around?

The other concern I have is I'd like consumers of my controller to use entity objects as POJOs without having to know or care if they are entities. But the rollback semantics means my callers have to deal with handling a rollback. Alternately I could pay the copy cost of detaching my objects before passing them up to higher levels, but then my caller will still have to deal with the semantics of detached objects (e.g. lazy fields or associated instances may be null). I don't see any way to expose entities directly to higher levels of my app that are entity-unaware... Which means I have to wrap my entities into proxy classes that handle all the JPA semantics internally and don't expose this to the caller.

I am concerned that the rollback consequences can slip past developers, who will then build apps that behave very erratically after a transaction rollback. I know it's in the spec, but having worked with lots of developers, most of them don't read the spec, but instead cut-and-paste from examples. It would be great if we did a blog about this, and provided some code showing how to do it right... I could do this, but before I do I thought I'd check with you all first for any thoughts you have on this.



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