#34819: GenericForeignKey.get_prefetch_queryset()
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Reporter: Richard Laager | Owner: nobody
Type: Bug | Status: new
Component: contrib.contenttypes | Version: 3.2
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 1
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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`get_prefetch_queryset()` returns two functions. The caller calls them
`rel_obj_attr` and `instance_attr`. They return a tuple of `(pk, cls)`.
They need to match so that objects can be pulled from the cache. In
`GenericForeignKey.get_prefetch_query()`, there is a bug where `gfk_key()`
(the `rel_obj_attr`) returns a `get_prep_value()`d value but the
`instance_attr` lambda returns `obj.pk`.
Accordingly, for objects where the prepped value and the Python
representation are not the same (e.g. the database uses a string and the
Python representation is an object instance), these will not match. This
makes things like
`Model.objects.prefetch_related('content_object').get(id=123)` clear (set
to `None`) the `content_object`.
The fix is to call `get_prep_value()` in the `instance_attr` code path.
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Ticket URL: <https://code.djangoproject.com/ticket/34819>
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