[hibernate-dev] What should happen to queued operations when a collection is detached?

[Gail Badner]

HHH-11209 involves a bug merging a detached entity with an uninitialized
collection that has queued operations.

After looking into this issue I found a bug
where AbstractPersistentCollection#operationQueue was not being cleared
after a commit, if there was no cascade mapped for the collection.

I've fixed that in a PR. [1]

After that fix, the detached entity in the test case attached to HHH-11209
has an uninitialized entity without any queued operations after commit,
which can be merged successfully in a new session/transaction.

There is still a problem when Hibernate tries to merge a detached entity
has an uninitialized collection with queued operations though. My PR throws
UnsupportedOperationException in this case, and there is a test case that
reproduces it.

I've been working on a fix to add support for this, but I have my doubts
that it really should be supported. I see that prior to fixing HHH-5855
(which caused HHH-11209), Hibernate simply ignored the queued operations in
the detached collection. [2].

The fix for HHH-5855 properly dealt with merging a managed collection that
was uninitialized with queued operations. It introduced the bug where a
NullPointerException would get thrown if that collection  was detached.

If we want to support merging the queued operations, then I would consider
that an improvement. Would this be a worthwhile improvement? I'm guessing
not, but I wanted to get some opinions.

For now, I see a couple of ways to deal with this so that HHH-11209 can be
wrapped up:
1) ignore queued operations in a detached collection when merging, as was
done before HHH-5855 was fixed.
2) clear the queued operations when the collection is detached.

Comments?

Thanks,
Gail

[1] https://github.com/hibernate/hibernate-orm/pull/2460
[2]
https://github.com/hibernate/hibernate-orm/commit/c1934b72edb4f781520937618b3b750bebb84576#diff-2c7912a47063b9ea81323bf9c6628895L651