Fixed #21612 -- Made QuerySet.update() respect to_field

1 files changed, 2 insertions, 2 deletions

diff --git a/django/db/models/base.py b/django/db/models/base.py
index f2404d40a5..2b79a20cee 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -826,10 +826,10 @@ class Model(six.with_metaclass(ModelBase)):
             setattr(self, cachename, obj)
         return getattr(self, cachename)
 
-    def prepare_database_save(self, unused):
+    def prepare_database_save(self, field):
         if self.pk is None:
             raise ValueError("Unsaved model instance %r cannot be used in an ORM query." % self)
-        return self.pk
+        return getattr(self, field.rel.field_name)
 
     def clean(self):
         """