#19722: GenericRelation in a subclass, filtering by a field of the GFK-declaring
model fails
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Reporter: ramiro | Owner: nobody
Type: Bug | Status: new
Component: contrib.contenttypes | Version: master
Severity: Normal | 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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This was report in a comment by user 'nator' to #11263, is a different
issue to the one initially discussed in that ticket. Quoting:
''Say we have a non-abstract superclass and a subclass, and we add a GR
relationship to the subclass:''
{{{
class Order(models.Model):
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
content_object = generic.GenericForeignKey()
status = models.CharField(max_length=10, default='ordered')
class Media(models.Model):
order = generic.GenericRelation(Order)
class Photo(Media):
title = models.CharField()
Photo.objects.filter(order__status='ordered').count()
--> doesn't break, but always returns 0.
}}}
''The basic problem is that when the Order object is created Django
inserts it into the DB using the content_type of Photo, but when the
select is run Django realizes Order actually lives in Media and tries to
use that content_type. So the inserts all "work", but the count() never
finds them. It's a mismatch between the content_type_id when it runs the
insert and select.
After digging through django/config/contenttypes/generic.py a bit I feel
like the correct answer is to change the inserts to use the content_type
of the class that actually contains the m2m relationship. (Media, in this
case).''
There is a proposed fix attached to that ticket.
--
Ticket URL: <https://code.djangoproject.com/ticket/19722>
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