r8586 fixed "View on Site" links for admin inline formsets, by having InlineAdminForm.__init__ set a temporary "content_type_id" attribute on the inline-edited "original" instance to the content type id of its model, and then using that attribute in the template to link to the redirection.
This is all fine and dandy, except when the model being edited inline already has a "content_type" field which is a foreign key to ContentType (most likely because it has a generic foreign key). In this case, InlineAdminForm reassigns an already-existing "content_type_id" attribute to point to the wrong model entirely, breaking any behavior of the instance that depends on the generic foreign key.
This behavior can be seen with these test models:
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic
class Parent(models.Model):
name = models.CharField(max_length=50)
def __unicode__(self):
return self.name
class Teacher(models.Model):
name = models.CharField(max_length=50)
def __unicode__(self):
return self.name
class Child(models.Model):
name = models.CharField(max_length=50)
teacher = models.ForeignKey(Teacher)
content_type = models.ForeignKey(ContentType)
object_id = models.PositiveIntegerField()
parent = generic.GenericForeignKey()
def __unicode__(self):
return u'I am %s, a child of %s' % (self.name, self.parent)
With this admin configuration:
from django.contrib import admin
from models import Child, Teacher, Parent
class ChildInline(admin.TabularInline):
model = Child
extra = 1
class TeacherAdmin(admin.ModelAdmin):
inlines = (ChildInline,)
admin.site.register(Teacher, TeacherAdmin)
admin.site.register(Parent)
In the admin, create a Parent named John, then create a Teacher named Sally, then add a Child named Joe using the inline formset for the Teacher. After saving the Child, where the new Child's unicode representation should be displayed as "I am Joe, a child of John", it will instead say "I am Joe, a child of I am Joe, a child of John". This is because InlineAdminForm has changed Joe's content_type_id from Parent to Child, so Joe's "parent" attribute is now pointing to himself.
(The reason for the Teacher model and FK in the above examples is to make it clear that this occurs with any ordinary InlineAdmin, not only with a GenericInlineAdmin).
The easy fix is to use a more obscure attribute name for the temporary "my content type" attribute needed for redirection. Technically it would still be possible to mistakenly overwrite an existing attribute, but much less likely than it is now.
naive fix with regression test