#19580: Unify reverse foreign key and m2m unsaved model querying
-------------------------------------+-------------------------------------
Reporter: Anssi Kääriäinen | Owner: raydeal
Type: | Status: closed
Cleanup/optimization |
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 1 | UI/UX: 0
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Changes (by Matt Westcott):
* cc: Matt Westcott (added)
Comment:
Ran across this while bringing Wagtail up to date with Django main. I
appreciate that accessing a reverse-FK relation on an unsaved instance is
undefined behaviour, so this isn't technically a breaking change -
however, I suspect there could be a lot of code in the wild that's doing
this unwittingly, in which case this change might be more disruptive than
expected.
For example, I had to make this fix:
https://github.com/wagtail/wagtail/pull/8028/commits/9e19bf63dbb698a4f57b131b6f8ae92bab7c2606
- where I'd implemented something approximating an InlineFormSet, but
neglected to make a special case for the 'create' view, and so it ends up
querying an unsaved instance to arrive at the initial empty formset. I
imagine this will be a fairly common gotcha in user code.
(for the record, Wagtail also does much more esoteric things with faking
relations on in-memory objects to support previews and saving drafts, but
I'm willing to take the hit for that :-) )
Should we consider making this a deprecation warning for now, and adding
the strict validation in Django 5.x instead? (Admittedly, this isn't the
sort of thing you can write a startup check for, so it may be that a
deprecation warning would only help for apps that have good test coverage
anyhow.)
--
Ticket URL: <https://code.djangoproject.com/ticket/19580#comment:56>
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