#34137: model.refresh_from_db() doesn't seem to clear cached generic foreign
keys
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Reporter: pascal chambon | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 3.2
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Description changed by pascal chambon:
Old description:
> In my code, Users have a generic foreign key like so:
>
> {{{
> controlled_entity_content_type = models.ForeignKey(ContentType,
> blank=True, null=True, on_delete=models.CASCADE)
> controlled_entity_object_id = models.PositiveIntegerField(blank=True,
> null=True)
> controlled_entity =
> GenericForeignKey("controlled_entity_content_type",
> "controlled_entity_object_id")
> }}}
>
> However, in unit-tests, when I refresh a user instance, the
> controlled_entity relation isn't cleared from cache, as can be seen here
> with IDs:
>
> {{{
> old_controlled_entity = authenticated_user.controlled_entity
> authenticated_user.refresh_from_db()
> new_controlled_entity = authenticated_user.controlled_entity
> assert id(old_controlled_entity) != id(new_controlled_entity) #
> FAILS
> }}}
>
> And this leads to subtle bugs like non-transitive equalities in tests :
>
> {{{
> assert authenticated_user.controlled_entity ==
> fixtures.client1_project2_organization3
> assert fixtures.client1_project2_organization3.get_pricing_plan()
> == pricing_plan
> assert authenticated_user.controlled_entity.get_pricing_plan() ==
> pricing_plan # FAILS
> }}}
>
> Calling "authenticated_user.controlled_entity.refresh_from_db()" solevd
> this particular bug, but "authenticated_user.refresh_from_db()" isn't
> enough.
>
> Tested under Django3.2.13 but the code of refresh_from_db() hasn't
> changed since then in Git's main branch (except few cosmetic adjustments
> on code format).
>
> I'm a bit lost in the code of refresh_from_db(), but I've just seen that
> the generic relation appears once in this loop, but is not considered as
> "cached" in the if() branch.
>
> {{{
> for field in self._meta.related_objects:
> #print("%% CLEARING RELATED FIELD", field)
> if field.is_cached(self):
> #print("%% DONE") # not called
> field.delete_cached_value(self)
> }}}
New description:
In my code, Users have a generic foreign key like so:
{{{
controlled_entity_content_type = models.ForeignKey(ContentType,
blank=True, null=True, on_delete=models.CASCADE)
controlled_entity_object_id = models.PositiveIntegerField(blank=True,
null=True)
controlled_entity =
GenericForeignKey("controlled_entity_content_type",
"controlled_entity_object_id")
}}}
However, in unit-tests, when I refresh a user instance, the
controlled_entity relation isn't cleared from cache, as can be seen here
with IDs:
{{{
old_controlled_entity = authenticated_user.controlled_entity
authenticated_user.refresh_from_db()
new_controlled_entity = authenticated_user.controlled_entity
assert id(old_controlled_entity) != id(new_controlled_entity) #
FAILS
}}}
And this leads to subtle bugs like non-transitive equalities in tests :
{{{
assert authenticated_user.controlled_entity ==
fixtures.client1_project2_organization3
assert fixtures.client1_project2_organization3.get_pricing_plan()
== pricing_plan
assert authenticated_user.controlled_entity.get_pricing_plan() ==
pricing_plan # FAILS
}}}
Calling "authenticated_user.controlled_entity.refresh_from_db()" solved
this particular bug, but "authenticated_user.refresh_from_db()" isn't
enough.
Tested under Django3.2.13 but the code of refresh_from_db() hasn't changed
since then in Git's main branch (except few cosmetic adjustments on code
format).
I'm a bit lost in the code of refresh_from_db(), but I've just seen that
the generic relation appears once in this loop, but is not considered as
"cached" in the if() branch.
{{{
for field in self._meta.related_objects:
#print("%% CLEARING RELATED FIELD", field)
if field.is_cached(self):
#print("%% DONE") # not called
field.delete_cached_value(self)
}}}
--
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Ticket URL: <https://code.djangoproject.com/ticket/34137#comment:1>
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