Ticket #13085: 13085.diff

django/contrib/contenttypes/generic.py

@@ -49 +49 @@
         # Convenience function using get_model avoids a circular import when
         # using this model
         ContentType = get_model("contenttypes", "contenttype")
-        if obj:
+        if obj is not None:
              return ContentType.objects.db_manager(obj._state.db).get_for_model(obj)
-        elif id:
+        elif id is not None:
              return ContentType.objects.db_manager(using).get_for_id(id)
         else:
             # This should never happen. I love comments like this, don't you?
@@ -72 +72 @@
             # performance when dealing with GFKs in loops and such.
             f = self.model._meta.get_field(self.ct_field)
             ct_id = getattr(instance, f.get_attname(), None)
-            if ct_id:
+            if ct_id is not None:
                 ct = self.get_content_type(id=ct_id, using=instance._state.db)
                 try:
                     rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))

tests/regressiontests/generic_relations_regress/tests.py

@@ -70 +70 @@
             Q(notes__note__icontains=r'other note'))
         self.assertTrue(org_contact in qs)
 
+    def test_if_eval_false(self):
+        """
+        Tests that generic relations work if the model instance evaluates to 
+        false e.g(len(obj) == 0).
 
+        Test for bug http://code.djangoproject.com/ticket/13085.
 
+        It does not test that generic objects work if content_type_id=0 but it
+        would be nice if it did.
+        """
+        # A group is created with no people as members.
+        # Since len(grp) == 0, due to no members, it will evaluate to False.
+        grp = GroupOfPeople(name='Those People')
+        grp.save()
+        note = Note.objects.create(note='They did it.', content_object=grp)
+        note.save()
+        # It would be nice to also test for adding a generic object with 
+        # content_type_id=0.  However there appears to be no content type
+        # with id=0 so it would be hard to make such a test.
+        

tests/regressiontests/generic_relations_regress/models.py

@@ -4 +4 @@
 
 __all__ = ('Link', 'Place', 'Restaurant', 'Person', 'Address', 
            'CharLink', 'TextLink', 'OddRelation1', 'OddRelation2', 
-           'Contact', 'Organization', 'Note')
+           'Contact', 'Organization', 'Note', 'GroupOfPeople')
 
 class Link(models.Model):
     content_type = models.ForeignKey(ContentType)
@@ -77 +77 @@
     name = models.CharField(max_length=255)
     contacts = models.ManyToManyField(Contact, related_name='organizations')
 
+
+# models for test_if_eval_false
+class GroupOfPeople(models.Model):
+    name = models.CharField(max_length=100)
+    people = models.ManyToManyField(Person)
+    
+    def __len__(self):
+        return self.people.all().count()