Made clear() on a reverse foreign key significantly more efficient. Thanks to Andrew Godwin for the review.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16335 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -459,9 +459,7 @@ class ForeignRelatedObjectsDescriptor(object):
                 remove.alters_data = True
 
                 def clear(self):
-                    for obj in self.all():
+                    self.update(**{rel_field.name: None})
-                        setattr(obj, rel_field.name, None)
-                        obj.save()
                 clear.alters_data = True
 
         manager = RelatedManager()

tests/modeltests/many_to_one/tests.py

@@ -1,10 +1,13 @@
+from copy import deepcopy
 from datetime import datetime
+
 from django.test import TestCase
 from django.core.exceptions import FieldError
+
 from models import Article, Reporter
 
-class ManyToOneTests(TestCase):
 
+class ManyToOneTests(TestCase):
     def setUp(self):
         # Create a few Reporters.
         self.r = Reporter(first_name='John', last_name='Smith', email='john@example.com')
@@ -368,5 +371,4 @@ class ManyToOneTests(TestCase):
         # Regression for #12876 -- Model methods that include queries that
         # recursive don't cause recursion depth problems under deepcopy.
         self.r.cached_query = Article.objects.filter(reporter=self.r)
-        from copy import deepcopy
         self.assertEqual(repr(deepcopy(self.r)), "<Reporter: John Smith>")

tests/modeltests/many_to_one_null/tests.py

@@ -1,8 +1,10 @@
+from __future__ import with_statement
+
 from django.test import TestCase
 from models import Reporter, Article
 
-class ManyToOneNullTests(TestCase):
 
+class ManyToOneNullTests(TestCase):
     def setUp(self):
         # Create a Reporter.
         self.r = Reporter(name='John Smith')
@@ -82,3 +84,11 @@ class ManyToOneNullTests(TestCase):
         self.assertQuerysetEqual(self.r.article_set.all(), [])
         self.assertQuerysetEqual(Article.objects.filter(reporter__isnull=True),
                                  ['<Article: First>', '<Article: Fourth>'])
+
+    def test_remove_efficiency(self):
+        r = Reporter.objects.create()
+        for _ in xrange(3):
+            r.article_set.create()
+        with self.assertNumQueries(1):
+            r.article_set.clear()
+        self.assertEqual(r.article_set.count(), 0)