Toplink ORM parent-child relationship (one-to-many assoc)

Question

Hello,
I'm having some problems changing the parent object of a child object. Can someone point me in the right direction?
the parent class:
public class Parent {
private List<Child> children;
the child class:
public class Child {
private ValueHolderInterface parent;
The children collection is privately owned by Parent.
the code to change the parent:
Child theChild = getTheChild();
Parent oldParent = theChild.getParent();
oldParent.getChildren().remove(theChild);
theChild.setParent(null);
Parent newParent = getTheNewParent();
theChild.setParent(newParent);
newParent.getChildren.add(theChild);
UnitOfWork uow = getSessionFactory().acquireUnitOfWork();
Object workingCopy = uow.readObject(theChild);
if (workingCopy == null) {
throw new RuntimeException("Could not find entity to update");
uow.deepMergeClone(theChild);
uow.commit();
The logs show that Toplink updates the parent_id of the child row (which I expect).
But after that Toplink deletes the child and then deletes the old parent (which I don't expect).
What is the correct way to update the parent of the child?

Answer 1

Hello,
Sounds like you have the bidirectional relationship set as privately owned on the child->parent relationship as well as on the parent->child.
I noticed in your code you are merging theChild into the uow, but not the oldParent. Depending on how you are getting theChild and oldParent objects (I hope you aren't making changes directly on objects in the cache), the changes to oldParent will not be picked up unless you merge them into the uow as well.
What looks like is happening is that when you null out the child->oldParent relation and then set a new parent, this forces TopLink to remove the oldParent (since I believe this relationship is privately owned). Since the oldParent still references theChild and the relationship is privately owned, theChild is also marked for deletion.
You might not want relationships marked as privately owned, since it indicates that the referenced objects cannot exist without the object referencing it. Unsetting the child->parent relation to be private owned should fix the problem, but you will still need to ensure the changes in oldParent are merged. I would suggest that right after you call getTheChild() you acquire a uow, read theChild and then work directly on the working copy instead of theChild object. This will remove the need to merge changes later. If that is not possible, just be sure to merge the oldParent in as well.
Best Regards,
Chris