Fixed #11956 -- Modified the handling of m2m relationships between subclasses. Thanks to nidi for the report, and astoneman for the suggestion on how to fix the problem.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12908 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -710,7 +710,7 @@ class ReverseManyRelatedObjectsDescriptor(object):
             model=rel_model,
             core_filters={'%s__pk' % self.field.related_query_name(): instance._get_pk_val()},
             instance=instance,
-            symmetrical=(self.field.rel.symmetrical and isinstance(instance, rel_model)),
+            symmetrical=self.field.rel.symmetrical,
             source_field_name=self.field.m2m_field_name(),
             target_field_name=self.field.m2m_reverse_field_name(),
             reverse=False
@@ -991,7 +991,7 @@ class ManyToManyField(RelatedField, Field):
         kwargs['rel'] = ManyToManyRel(to,
             related_name=kwargs.pop('related_name', None),
             limit_choices_to=kwargs.pop('limit_choices_to', None),
-            symmetrical=kwargs.pop('symmetrical', True),
+            symmetrical=kwargs.pop('symmetrical', to==RECURSIVE_RELATIONSHIP_CONSTANT),
             through=kwargs.pop('through', None))
 
         self.db_table = kwargs.pop('db_table', None)

tests/regressiontests/m2m_regress/models.py

@@ -17,6 +17,13 @@ class Tag(models.Model):
     def __unicode__(self):
         return self.name
 
+# Regression for #11956 -- a many to many to the base class
+class TagCollection(Tag):
+    tags = models.ManyToManyField(Tag, related_name='tag_collections')
+
+    def __unicode__(self):
+        return self.name
+
 # A related_name is required on one of the ManyToManyField entries here because
 # they are both addressable as reverse relations from Tag.
 class Entry(models.Model):
@@ -102,5 +109,17 @@ FieldError: Cannot resolve keyword 'porcupine' into field. Choices are: id, name
 >>> w.save()
 >>> w.delete()
 
+# Regression for #11956 -- You can add an object to a m2m with the
+# base class without causing integrity errors
+>>> c1 = TagCollection.objects.create(name='c1')
+>>> c1.tags = [t1,t2]
+
+>>> c1 = TagCollection.objects.get(name='c1')
+>>> c1.tags.all()
+[<Tag: t1>, <Tag: t2>]
+
+>>> t1.tag_collections.all()
+[<TagCollection: c1>]
+
 """
 }