DeepMergeClone problem with unsolicited updates

Question

Hi,
I am having an odd problem with deepMergeClone and was hoping someone could point me in the correct direction. I am using Weblogic, WebLogicJTSExternalTransactionController, and TopLink 4.6.
My object model is something like:
Organization
- Address
- Employees(collection of Person)
- Name, etc...
Person
- Address
- Name, etc...
Address
- Region
- Country
- Street1, etc...
The application uses Session Beans that provide TopLink mapped objects to a Servlet layer using Struts. The objects are updated, created, etc. in the Struts actions and then sent to the Session Beans. In the Session Bean we do the something like
ExternalTransactionController controller = session.getExternalTransactionController();
UnitOfWork uow = uow = controller.getActiveUnitOfWork();
uow.readObject(obj); //ensure obj is cached and registered
uow.deepMergeClone(obj);
Here is my problem: In the Struts layer, I read a organization by id for an update.
Updating an organization.address.region will sometimes cause an update to multiple employee's address.region. If you look at the object heirarchy before it gets passed into deepMergeClone, everything looks great.
If I add code to read the address by id for the organization.address and then set the address into the organization, the update seems to work as expected.
Is there some rule about needing to register nested objects prior to deepMergeClone? Any other thoughts on what I might be doing wrong?
Tom

Answer 1

DeepMergeClone is a very useful feature of TopLink as it allows the application to not have to be concerned with what it changes on the client. The client can traverse any relationships of the objects that are serialized to it (provided the relationships were serialized) and make whatever changes to whatever objects it desires. It can then send the entire object graph back to the server which can does not have to be aware of what the client was doing and can just deepMergeClone everything back into a unit of work and commit the changes to the database.
Unfortunately the main benefit of deepMergeClone can also be its biggest issue when something goes wrong. DeepMergeClone traverses "everything" related to an object and merges "everything", for complex objects this can occasionally lead to the merging of changes that were not intended or desired by the client.
Examples can include:
- Transient attributes. These will be serialized as null so will be merged as null into the unit of work causing incorrect updates to null.
- Duplicate objects and loss of object identity. Since TopLink is not running on the client, it is possible for the client to violate object identity through retrieving two separately serialized objects from the server that contain relationships to the same object. If these two objects are then related and serialized back to the server and deepMergeClone'd, TopLink will be given two different versions of the same object, this object can be merged twice and one copy can overwrite the other copy. This may be what is occurring with the problem at the start of this thread.
There is another thread with a similar issue that also links to another thread that has a good description of each of the unit of work merge APIs.
Re: 1-M deepMergeClone leaves old items in DB
In general deepMergeClone is a very useful feature, and if you are using it successfully definitely don't stop using it. But if you commonly experience problems, or performance issues, you may wish the consider one of the other merge APIs that give the application more control over what is and is not merged.
If you are still experiencing the problem and have verified that you are not violating object identity, you will probably need to contact technical support to have them investigate your issue in more detail.