Ticket #18556: t18556-remove-efficiency.diff

django/db/models/fields/related.py

@@ -523 +523 @@
             if rel_field.null:
                 def remove(self, *objs):
                     val = getattr(self.instance, attname)
+                    ids = []
                     for obj in objs:
                         # Is obj actually part of this descriptor set?
                         if getattr(obj, rel_field.attname) == val:
-                            setattr(obj, rel_field.name, None)
-                            obj.save()
+                            ids.append(obj.pk)
                         else:
                             raise rel_field.rel.to.DoesNotExist("%r is not related to %r." % (obj, self.instance))
+                    self.filter(pk__in=ids).update(**{rel_field.name: None})
                 remove.alters_data = True
 
                 def clear(self):

django/db/models/related.py

@@ -36 +36 @@
                 {'%s__isnull' % self.parent_model._meta.module_name: False})
         lst = [(x._get_pk_val(), smart_unicode(x)) for x in queryset]
         return first_choice + lst
-        
+
     def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
         # Defer to the actual field definition for db prep
         return self.field.get_db_prep_lookup(lookup_type, value,

tests/modeltests/many_to_one_null/tests.py

@@ -92 +92 @@
             r.article_set.create()
         with self.assertNumQueries(1):
             r.article_set.clear()
-        self.assertEqual(r.article_set.count(), 0)
- No newline at end of file
+        self.assertEqual(r.article_set.count(), 0)
+
+    def test_remove_efficiency(self):
+        r = Reporter.objects.create()
+        articles = []
+        for _ in xrange(3):
+            articles.append(r.article_set.create())
+        with self.assertNumQueries(1):
+            r.article_set.remove(*articles)
+        self.assertEqual(r.article_set.count(), 0)