Fixed #7778 -- Fixed a tricky case of foreign key clearing with inherited

models. Patch from James Murty.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8100 bcc190cf-cafb-0310-a4f2-bffc1f526a37

AUTHORS

@@ -280,6 +280,7 @@ answer newbie questions, and generally made Django that much better:
     Eric Moritz <http://eric.themoritzfamily.com/>
     mrmachine <real.human@mrmachine.net>
     Robin Munn <http://www.geekforgod.com/>
+    James Murty
     msundstr
     Robert Myers <myer0052@gmail.com>
     Nebojša Dorđević

django/db/models/query.py

@@ -836,7 +836,9 @@ def delete_objects(seen_objs):
 
         update_query = sql.UpdateQuery(cls, connection)
         for field in cls._meta.fields:
-            if field.rel and field.null and field.rel.to in seen_objs:
+            if (field.rel and field.null and field.rel.to in seen_objs and
+                    filter(lambda f: f.column == field.column,
+                    field.rel.to._meta.fields)):
                 update_query.clear_related(field, pk_list)
 
     # Now delete the actual data.

tests/regressiontests/queries/models.py

@@ -190,6 +190,19 @@ class CustomPk(models.Model):
 class Related(models.Model):
     custom = models.ForeignKey(CustomPk)
 
+# An inter-related setup with a model subclass that has a nullable
+# path to another model, and a return path from that model.
+
+class Celebrity(models.Model):
+    name = models.CharField("Name", max_length=20)
+    greatest_fan = models.ForeignKey("Fan", null=True, unique=True)
+
+class TvChef(Celebrity):
+    pass
+
+class Fan(models.Model):
+    fan_of = models.ForeignKey(Celebrity)
+
 
 __test__ = {'API_TESTS':"""
 >>> t1 = Tag.objects.create(name='t1')
@@ -836,6 +849,21 @@ related via ForeignKeys.
 >>> len(Note.objects.order_by('extrainfo__info').distinct())
 3
 
+Bug #7778 - Model subclasses could not be deleted if a nullable foreign key
+relates to a model that relates back.
+
+>>> num_celebs = Celebrity.objects.count()
+>>> tvc = TvChef.objects.create(name="Huey")
+>>> Celebrity.objects.count() == num_celebs + 1
+True
+>>> f1 = Fan.objects.create(fan_of=tvc)
+>>> f2 = Fan.objects.create(fan_of=tvc)
+>>> tvc.delete()
+
+# The parent object should have been deleted as well.
+>>> Celebrity.objects.count() == num_celebs
+True
+
 """}
 
 # In Python 2.3, exceptions raised in __len__ are swallowed (Python issue