Ticket #14368: ticket-14368.patch

django/db/models/fields/related.py

@@ -253 +253 @@
                 if not router.allow_relation(value, instance):
                     raise ValueError('Cannot assign "%r": instance is on database "%s", value is on database "%s"' %
                                         (value, instance._state.db, value._state.db))
+            # Since we already know what the related object is, seed the related
+            # object caches now, too. This avoids another db hit if you get the
+            # object you just set.
+            setattr(instance, self.cache_name, value)
+            setattr(value, self.related.field.name, instance)
+        else:
+            # update the cached related instance (if any) and clear the cache
+            try:
+                rel_obj = getattr(instance, self.cache_name)
+            except AttributeError:
+                pass
+            else:
+                delattr(instance, self.cache_name)
+                setattr(rel_obj, self.related.field.name, None)
 
-        # Set the value of the related field to the value of the related object's related field
-        setattr(value, self.related.field.attname, getattr(instance, self.related.field.rel.get_related_field().attname))
-
-        # Since we already know what the related object is, seed the related
-        # object caches now, too. This avoids another db hit if you get the
-        # object you just set.
-        setattr(instance, self.cache_name, value)
-        setattr(value, self.related.field.get_cache_name(), instance)
+        if self.related.field.null:
+            # break the link to the existing value (if any)
+            filter_params = {self.related.field.name: instance._get_pk_val()}
+            update_params = {self.related.field.name: None}
+            db = router.db_for_write(self.related.model, instance=instance)
+            self.related.model._base_manager.using(db).filter(**filter_params).update(**update_params)
 
 class ReverseSingleRelatedObjectDescriptor(object):
     # This class provides the functionality that makes the related-object

tests/regressiontests/one_to_one_regress/tests.py

@@ -128 +128 @@
                 Target.objects.exclude(pointer2=None),
                 []
         )
+
+    def test_modify_related(self):
+        """
+        Setting the reverse relationship of a O2O null field to a new instance
+        should succeed and remove the link from the current instance (if any).
+        """
+        b1 = UndergroundBar.objects.create(place=self.p1, serves_cocktails=False)
+        b2 = UndergroundBar(serves_cocktails=True)
+        self.p1.undergroundbar = b2
+        b2.save()
+        self.assertEqual(UndergroundBar.objects.get(pk=b1.pk).place, None)
+        self.assertEqual(UndergroundBar.objects.get(pk=b2.pk).place, self.p1)
+
+    def test_unset_related(self):
+        """Regression test for #14368 [1]
+
+        Setting the reverse relationship of a O2O null field to None should
+        succeed and remove the link from the current instance (if any).
+        """
+        bar = UndergroundBar.objects.create(place=self.p1, serves_cocktails=False)
+        self._unset_related(self.p1, bar)
+
+    def test_unset_related_after_set(self):
+        """Regression test for #14368 [2]
+
+        Setting the reverse relationship of a O2O null field to None should
+        succeed and remove the link from the current instance (if any).
+
+        In this test the related object is set to point to an instance before
+        set to None.
+        """
+        bar = UndergroundBar(serves_cocktails=False)
+        self.p1.undergroundbar = bar
+        bar.save()
+        self._unset_related(self.p1, bar)
+        self.assertEqual(bar.place, None)
+
+    def _unset_related(self, place, undergroundbar):
+        self.assertEqual(UndergroundBar.objects.filter(place=place).count(), 1)
+        self.assertEqual(place.undergroundbar, undergroundbar)
+        place.undergroundbar = None
+        self.assertEqual(UndergroundBar.objects.filter(place=place).count(), 0)
+        self.assertRaises(UndergroundBar.DoesNotExist, getattr, place, 'undergroundbar')