#33984: Related managers cache gets stale after saving a fetched model with new
PK
-------------------------------------+-------------------------------------
Reporter: joeli | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 4.1
(models, ORM) |
Severity: Release blocker | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Keryn Knight):
In ''theory'' the "simplest" solution (to keep the caching behaviour and
allow the documented duplication method) is to special-case `None` as a pk
value and always instantiate a fresh manager, circumventing the cache
entirely.
I think though that the problem ''technically'' extends further, any
change to the `pk` -- or more specifically, the manager's core filter
dependencies -- would become stale subsequently. Unsupported those other
cases may be from a documentation standpoint, but I'm sure someone
somewhere is doing it...
If there's a path where we (I) can invalidate correctly, and it keeps the
overall improvement of #32980, and it's not too invasive or complex, we
can try and proceed on that basis. If the change restores the ''old''
performance behaviour in the process, there's not much argument (except
maybe memory pressure/garbage collection) to keeping the cache
functionality, off the top of my head.
Basically there's two things to check there above, and if either of them
is a miss, I guess we'd revert #32980 because I can envisage ''plenty'' of
cases where people use the `pk=None` trick to clone an instance,
documented as it is.
I may assign this out to myself in the near future if it's otherwise not
picked up, assuming I can find the availability.
--
Ticket URL: <https://code.djangoproject.com/ticket/33984#comment:6>
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