Exception during MergeClone in Nested UOW

Question

I have defined an object model with objA -- 1..1 --> objB.
Then, in the business logic, I try to create objA and objB in nested UOW, psudo code as follows:
UOWParent = session.acquireUOW();
UOWinner1 = UOWParent.acquireUOW();
objB = new ObjectB;
UOWinner1.mergeCloneWithReference(objB);
UOWinner1.commit();
UOWinner2 = UOWParent.acquireUOW();
objA = new ObjectA;
objA.B = objB;
UOWinner2.mergeCloneWithReference(objA);
UOWinner2.commit();
UOWParent.commit();
(OracleAS TopLink - 10g (9.0.4.9) (Build 060118)): oracle.toplink.exceptions.QueryException Exception Description: The object [com.domain.model.ContainerGroup@191f61c], of class [class com.domain.model.ContainerGroup], with identity hashcode (System.identityHashCode()) [26,342,940], is the original to a registered new object. The UnitOfWork clones registered new objects, so you must ensure that an object is registered before it is referenced by another object. If you do not want the new object to be cloned, use the UnitOfWork.registerNewObject(Object) API. If you are still having problems, you can use the UnitOfWork.validateObjectSpace() method to help debug where the error occurred. For more information, see the manual or FAQ. at oracle.toplink.exceptions.QueryException.backupCloneIsOriginalFromSelf(QueryException.java:160) at oracle.toplink.publicinterface.UnitOfWork.getBackupClone(UnitOfWork.java:1549) at oracle.toplink.publicinterface.UnitOfWork.calculateChanges(UnitOfWork.java:438) at oracle.toplink.publicinterface.UnitOfWork.commitToDatabaseWithChangeSet(UnitOfWork.java:1134) at oracle.toplink.publicinterface.UnitOfWork.commitRootUnitOfWork(UnitOfWork.java:955) at oracle.toplink.publicinterface.UnitOfWork.commit(UnitOfWork.java:770) at org.springframework.orm.toplink.TopLinkTransactionManager.doCommit(TopLinkTransactionManager.java:399) ... 38 more
If I use the returned object from "UOWinner1.mergeCloneWithReference(objB);", and use this object for "objA.B = objB;" instead during the second transaction, the exception disappeared and the records can be updated successfully in DB
My Question is...
1) What's meant by the exception"oracle.toplink.exceptions.QueryException.backupCloneIsOriginalFromSelf"?
2) What is the object returned by mergeClone? is it a Session Cached object, or a working Clone registered with UOWinner1?
3) Actually, what's going on during mergeClone? Why the exception thrown is a "QueryException"?
Message was edited by:
zolobag

Answer 1

Why are you using mergeCloneWithReferences when you are creating an object, you would probably be interested in running
uow.registerObject(persistentObj);
uow.assignSequenceNumbers();
A merge clone is if you have an object in the database and a new version from the app/gui. mergeClone lets you merge the changes in via toplink. Toplink is matching references and other assorted items to see what the changeset it and then issues the approptiate SQL to correct it. Remember that you must not read an item out of the session cache, modify it and try to merge clone it via UOW since that is not correct.
From API:
mergeCloneWithReferences
PUBLIC: Merge the attributes of the clone into the unit of work copy. This can be used for objects that are returned from the client through RMI serialization (or another serialization mechanism), because the RMI object will be a clone this will merge its attributes correctly to preserve object identity within the unit of work and record its changes. The object and its private owned parts are merged. This will include references from this clone to independent objects.
Returns:
the registered version for the clone being merged.