Fix dealing with missing derived table data with new prefetching code

polymorphic/query.py

@@ -364,6 +364,7 @@ class PolymorphicQuerySet(QuerySet):
                     # upcast it and put it in the results
                     resultlist.append(transmogrify(real_concrete_class, base_object))
                 else:
+                    # This model has a concrete derived class, track it for bulk retrieval.
                     real_concrete_class = content_type_manager.get_for_id(real_concrete_class_id).model_class()
                     idlist_per_model[real_concrete_class].append(getattr(base_object, pk_name))
                     indexlist_per_model[real_concrete_class].append((i, len(resultlist)))
@@ -416,7 +417,12 @@ class PolymorphicQuerySet(QuerySet):
             for i, j in indices:
                 base_object = base_result_objects[i]
                 o_pk = getattr(base_object, pk_name)
-                real_object = copy.copy(real_objects_dict[o_pk])
+                real_object = real_objects_dict.get(o_pk)
+                if real_object is None:
+                    continue
+
+                # need shallow copy to avoid duplication in caches (see PR #353)
+                real_object = copy.copy(real_object)
                 real_class = real_object.get_real_instance_class()
 
                 # If the real class is a proxy, upcast it

polymorphic/tests/test_orm.py

@@ -347,28 +347,32 @@ class PolymorphicTests(TransactionTestCase):
     def test_queryset_missing_derived(self):
         a = Model2A.objects.create(field1='A1')
         b = Model2B.objects.create(field1='B1', field2='B2')
+        c = Model2C.objects.create(field1='C1', field2='C2', field3='C3')
         b_base = Model2A.objects.non_polymorphic().get(pk=b.pk)
+        c_base = Model2A.objects.non_polymorphic().get(pk=c.pk)
 
         b.delete(keep_parents=True)  # e.g. table was truncated
 
-        qs1 = Model2A.objects.order_by('field1').non_polymorphic()
-        qs2 = Model2A.objects.order_by('field1').all()
+        qs_base = Model2A.objects.order_by('field1').non_polymorphic()
+        qs_polymorphic = Model2A.objects.order_by('field1').all()
 
-        self.assertEqual(list(qs1), [a, b_base])
-        self.assertEqual(list(qs2), [a])
+        self.assertEqual(list(qs_base), [a, b_base, c_base])
+        self.assertEqual(list(qs_polymorphic), [a, c])
 
     def test_queryset_missing_contenttype(self):
         stale_ct = ContentType.objects.create(app_label='tests', model='nonexisting')
         a1 = Model2A.objects.create(field1='A1')
         a2 = Model2A.objects.create(field1='A2')
+        c = Model2C.objects.create(field1='C1', field2='C2', field3='C3')
+        c_base = Model2A.objects.non_polymorphic().get(pk=c.pk)
 
         Model2B.objects.filter(pk=a2.pk).update(polymorphic_ctype=stale_ct)
 
-        qs1 = Model2A.objects.order_by('field1').non_polymorphic()
-        qs2 = Model2A.objects.order_by('field1').all()
+        qs_base = Model2A.objects.order_by('field1').non_polymorphic()
+        qs_polymorphic = Model2A.objects.order_by('field1').all()
 
-        self.assertEqual(list(qs1), [a1, a2])
-        self.assertEqual(list(qs2), [a1, a2])
+        self.assertEqual(list(qs_base), [a1, a2, c_base])
+        self.assertEqual(list(qs_polymorphic), [a1, a2, c])
 
     def test_translate_polymorphic_q_object(self):
         self.create_model2abcd()
@@ -1056,7 +1060,6 @@ class PolymorphicTests(TransactionTestCase):
                 MultiTableDerived(field1='field1', field2='field2')
             ])
 
-
     def test_can_query_using_subclass_selector_on_abstract_model(self):
         obj = SubclassSelectorAbstractConcreteModel.objects.create(concrete_field='abc')
 
@@ -1078,8 +1081,26 @@ class PolymorphicTests(TransactionTestCase):
     def test_prefetch_related_behaves_normally_with_polymorphic_model(self):
         b1 = RelatingModel.objects.create()
         b2 = RelatingModel.objects.create()
-        a = b1.many2many.create()
-        b2.many2many.add(a)
+        a = b1.many2many.create()  # create Model2A
+        b2.many2many.add(a)  # add same to second relating model
         qs = RelatingModel.objects.prefetch_related('many2many')
         for obj in qs:
             self.assertEqual(len(obj.many2many.all()), 1)
+
+    def test_prefetch_related_with_missing(self):
+        b1 = RelatingModel.objects.create()
+        b2 = RelatingModel.objects.create()
+
+        rel1 = Model2A.objects.create(field1='A1')
+        rel2 = Model2B.objects.create(field1='A2', field2='B2')
+
+        b1.many2many.add(rel1)
+        b2.many2many.add(rel2)
+
+        rel2.delete(keep_parents=True)
+
+        qs = RelatingModel.objects.order_by('pk').prefetch_related('many2many')
+        objects = list(qs)
+        self.assertEqual(len(objects[0].many2many.all()), 1)
+        self.assertEqual(len(objects[1].many2many.all()), 0)  # derived object was not fetched
+        self.assertEqual(len(objects[1].many2many.non_polymorphic()), 1)  # base object does exist