#28856: GenericForeignKey attributes create new instances on every access
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Reporter: Morgan Wahl | Owner: nobody
Type: Bug | Status: new
Component: contrib.contenttypes | Version: 1.10
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by Simon Charette):
* has_patch: 0 => 1
* stage: Unreviewed => Accepted
Comment:
Thanks Morgan, I missed that! This is quite a complex scenario: GFK, PK
type mismatch, and MTI so I'm not surprised it broke given the small
number of tests for PK type coercion.
The culprit seems to be that related fields don't delegate `to_python` to
the field they reference so the `OtherSub` primary key, a `OneToOneField`,
uses the default `Field.to_python` which is an identity function. This
causes
[https://github.com/django/django/blob/b9f8635f58ad743995cad2081b3dc395e55761e5/django/contrib/contenttypes/fields.py#L234
this line] to be falsey because `rel_obj._meta.pk.to_python('1')` returns
`'1'` instead of `1`.
I feel like the correct way to solve that would to implement
`ForeignKey.to_python` (which `OneToOneField` subclasses) to use
`self.foreign_related_fields[0].to_python` but even if this causes a
single failure in the test suite I feel like this would be to intrusive
for a backport. What I'd favor doing instead is implementing this approach
in master and adapt `GenericForeignKey.__get__` to work around the issue
if a backport is deemed eligible.
Here's a PR for master: https://github.com/django/django/pull/9395
And one for 1.11.x if you judge it should be backported Tim:
https://github.com/django/django/pull/9396
--
Ticket URL: <https://code.djangoproject.com/ticket/28856#comment:5>
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