Opened 16 years ago

Closed 10 years ago

#7551 closed Bug (fixed)

GenericForeignKey fails if initialized to None during model init

Reported by: Sam Bull Owned by: Bouke Haarsma
Component: contrib.contenttypes Version: dev
Severity: Normal Keywords: contenttypes genericforeignkey
Cc: sbull@… Triage Stage: Accepted
Has patch: yes Needs documentation: no
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no

Description (last modified by Ramiro Morales)

Supposing you have a model with a GenericForeignKey...

class Example(models.Model):
    name = models.CharField()
    content_type = models.ForeignKey(ContentType, null=True, blank=True)
    object_id = models.PositiveIntegerField(null=True, blank=True)
    obj = GenericForeignKey()

If you initialize like this, everything is fine:

ex = Example(name='foobar')

But if you do this...

ex = Example(name='foobar', obj=None)

You get an exciting error:
Impossible arguments to GFK.get_content_type!

It looks like the GFK tries to initialize the content_type and object_id fields if its attribute is one of the ones passed to the init. In fact, it should follow the example of get and only initialize those fields if the argument passed to it is non-None.

Attachments (2)

fix_for_content_type_bug.diff (681 bytes ) - added by Sam Bull 16 years ago.
GFK-init patch
fix_for_content_type_bug_improved.diff (639 bytes ) - added by Sam Bull 16 years ago.
revised patch

Download all attachments as: .zip

Change History (17)

by Sam Bull, 16 years ago

GFK-init patch

comment:1 by Sam Bull, 16 years ago

Cc: sbull@… added

Gah, I realized my ct and obj_id fields in the example won't work with the GFK field unless I tell it what they're called. This is a bug in my example, my original code properly identifies the content type and object id fields to the GFK.

comment:2 by Eric Holscher, 16 years ago

milestone: 1.0
Patch needs improvement: set
Triage Stage: UnreviewedAccepted

comment:3 by edrex, 16 years ago

Owner: changed from nobody to edrex

comment:4 by edrex, 16 years ago

Owner: edrex removed

comment:5 by James Bennett, 16 years ago

milestone: 1.0post-1.0

This feels like enough of an edge case (knowingly passing None when you could just leave it out of the argument list to the constructor) that it can wait a bit.

by Sam Bull, 16 years ago

revised patch

comment:6 by Sam Bull, 16 years ago

I've tried to provide a better patch.

I agree that this is an unusual situation, but it can cause hard to debug errors. The problem is that you might be passing in an object via the model's constructor and not know if it's None or not.

Null GFK fields are allowed, so passing in a value that might be None should be allowed as well.

I do agree that this may not be needed for 1.0, but I wanted to highlight the problems this bug causes.

comment:7 by (none), 15 years ago

milestone: post-1.0

Milestone post-1.0 deleted

comment:8 by Gabriel Hurley, 13 years ago

Component: Contrib appscontrib.contenttypes

comment:9 by Luke Plant, 13 years ago

Severity: Normal
Type: Bug

comment:10 by Aymeric Augustin, 12 years ago

UI/UX: unset

Change UI/UX from NULL to False.

comment:11 by Aymeric Augustin, 12 years ago

Easy pickings: unset

Change Easy pickings from NULL to False.

comment:12 by Ramiro Morales, 11 years ago

Description: modified (diff)

comment:13 by Ramiro Morales, 11 years ago

See also #18599.

comment:14 by Bouke Haarsma, 10 years ago

Owner: set to Bouke Haarsma
Status: newassigned

I've improved on this patch by also checking if None is allowed as the foreign key. Previous patches just ignored None, but that doesn't seem right as sometimes None is really invalid, for example when the GFK is non-optional. See my PR: https://github.com/django/django/pull/1753.

comment:15 by Tim Graham <timograham@…>, 10 years ago

Resolution: fixed
Status: assignedclosed

In 3918eeb9fde03a2ad1941bce022615fff8eae34d:

Fixed #7551 -- Made GFK allow None init argument.

Thanks SamBull for the report.

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