Admin Error when subclassing ContentType for generic Relations

[MS]

If you subclass the ContentType with a proxy model, for example to use other ordering or change some other Meta options, you will get an error in the Admin interface, when using GenericTabularInline.

The problem is line 357 in ​http://code.djangoproject.com/browser/django/trunk/django/contrib/contenttypes/generic.py, where the test is with equal but should be subcalss instead.

Example in models:

from django.db import models
from django.contrib.contenttypes import generic
from django.contrib.contenttypes.models import ContentType as CT

class ContentType(CT):

    class Meta:
        proxy = True
        ordering = ('app_label', 'model')

class ModelWithGeneric(models.Model):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    contentObject = generic.GenericForeignKey('content_type', 'object_id')

class ObjectWithGeneric(models.Model):
    media = generic.GenericRelation(ModelWithGeneric, content_type_field='content_type', object_id_field='object_id')

Example in Admin:

from django.contrib.contenttypes import generic
from django.contrib import admin

from apps.models import *

class GenericInlineAdmin(generic.GenericTabularInline):
    model = ModelWithGeneric


class ObjectAdmin(admin.ModelAdmin):
    inlines = (
        GenericInlineAdmin,
    )
admin.site.register(ObjectWithGeneric, ObjectAdmin)

Error is: fk_name '<django.db.models.fields.related.ForeignKey object at 0x0319A1F0>' is not a ForeignKey to ContentType

[Russell Keith-Magee]

The line is now 374, inside generic_inlineformset_factory.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Mariusz Felisiak]

ContentType subclasses are not supported and raised contenttypes.E004 since Django 1.7 (see d818e0c9b2b88276cc499974f9eee893170bf0a8).