Ticket #2160: 0_pk.2.patch

django/db/models/base.py

@@ -167 +167 @@
 
         # First, try an UPDATE. If that doesn't update anything, do an INSERT.
         pk_val = self._get_pk_val()
-        pk_set = bool(pk_val)
+        pk_set = bool(pk_val) or pk_val == 0
         record_exists = True
         if pk_set:
             # Determine whether a record with the primary key already exists.

docs/db-api.txt

@@ -142 +142 @@
 or ``UPDATE`` SQL statements. Specifically, when you call ``save()``, Django
 follows this algorithm:
 
-    * If the object's primary key attribute is set to a value that evaluates to
-      ``True`` (i.e., a value other than ``None`` or the empty string), Django 
-      executes a ``SELECT`` query to determine whether a record with the given 
-      primary key already exists.
+    * If the object's primary key attribute is set to a value that equals ``0``
+      or evaluates to ``True`` (i.e., a value other than ``None`` or the empty
+      string), Django executes a ``SELECT`` query to determine whether a record
+      with the given primary key already exists.
     * If the record with the given primary key does already exist, Django
       executes an ``UPDATE`` query.
     * If the object's primary key attribute is *not* set, or if it's set but a