Ticket #14368: 14368.patch

django/db/models/fields/related.py

@@ -254 +254 @@
                     raise ValueError('Cannot assign "%r": instance is on database "%s", value is on database "%s"' %
                                         (value, instance._state.db, value._state.db))
 
-        # 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))
+        if value is not 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)
+        else:
+            value = getattr(instance, self.related.var_name, None)
+            if value is not None:
+                setattr(value, self.related.field.name, None)
+            try:
+                delattr(instance, self.cache_name)
+            except AttributeError:
+                pass
 
-        # 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)
-
 class ReverseSingleRelatedObjectDescriptor(object):
     # This class provides the functionality that makes the related-object
     # managers available as attributes on a model class, for fields that have

tests/modeltests/one_to_one/tests.py

@@ +1 @@
+from django.test import TestCase
+
+from models import First, Second
+
+class OneToOneTestCase(TestCase):
+    
+    def test_set_related_to_none(self):
+        # regression test for #14368
+        first = First.objects.create()
+        second = Second.objects.create()
+        first.second = second
+        first.second = None
+        self.assertRaises(Second.DoesNotExist, getattr, first, 'second')
+        self.assert_(second.first is None)

tests/modeltests/one_to_one/models.py

@@ -46 +46 @@
     def __unicode__(self):
         return u"Multimodel %s" % self.name
 
+class First(models.Model):
+    pass
+
+class Second(models.Model):
+  first = models.OneToOneField(First, null=True)
+
 __test__ = {'API_TESTS':"""
 # Create a couple of Places.
 >>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton')
@@ -190 +196 @@
 ...         print "Fail with %s" % type(e)
 Pass
 >>> transaction.savepoint_rollback(sid)
-
 """}