id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27740	Allow content_type or object_id of GenericForeignKey to be field on related model	Chris Morbitzer	nobody	"I would like to specify a related model field as the values of content_type or object_id of GenericForeignKey. For example:

{{{
class Widget(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)

class Gadget(models.Model):
    widget = models.ForeignKey(Widget, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('widget__content_type', 'object_id')
}}}

If I tried to use this now, I would get the error:
{{{
Traceback (most recent call last):
  File ""django/db/models/options.py"", line 617, in get_field
    return self.fields_map[field_name]
KeyError: 'widget__content_type'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ""django/contrib/contenttypes/fields.py"", line 224, in __get__
    f = self.model._meta.get_field(self.ct_field)
  File ""django/db/models/options.py"", line 619, in get_field
    raise FieldDoesNotExist('%s has no field named %r' % (self.object_name, field_name))
django.core.exceptions.FieldDoesNotExist: Gadget has no field named 'widget__content_type'
}}}
One use case for this is a generic custom attribute system, where attribute fields can be created for any other model. The ""fields"" model has the content_type field. The ""values"" model has the object ID and value fields. The developer would like to query the object that the ""values"" record references: value.content_object"	New feature	closed	contrib.contenttypes	1.10	Normal	wontfix			Unreviewed	0	0	0	0	0	0