#2259: PK Change creates new object instead of update
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Reporter: [email protected] | Owner: nobody
Status: reopened | Milestone:
Component: django.contrib.admin | Version:
Resolution: | Keywords:
Stage: Design decision needed | Has_patch: 0
Needs_docs: 1 | Needs_tests: 0
Needs_better_patch: 1 |
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Changes (by carljm):
* stage: Accepted => Design decision needed
Comment:
So after looking at this a bit on the flight yesterday, the tricky bit
turns out to be referential integrity. As in, updating a PK breaks it, if
there are any foreign keys pointing to that row. Which results in broken
foreign keys on databases that don't enforce referential integrity, and an
immediate IntegrityError on databases that do.
For databases that support it, ON UPDATE CASCADE would fix this (which
would mean this ticket blocks on #7539). Otherwise, we could manually
emulate ON UPDATE CASCADE, which doen't actually sound terribly onerous
(one query per referencing table), but is likely to be somewhat fiddly in
practice and kinda gives me the willies.
I don't see it as a viable option to provide a "feature" in the admin that
breaks referential integrity in your database. So setting this back to
DDN.
I do have a patch that works fine, aside from the referential integrity
problem, which I'll upload. I added an optional argument to Model.save()
rather than using the .update() trick so as to make it work without adding
any additional queries. This choice would be easy to reverse if the
additional save arg is unacceptable, but not going to bother with that
until the bigger issues are resolved.
--
Ticket URL: <http://code.djangoproject.com/ticket/2259#comment:18>
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