Fixed #2512 -- Fixed SQL error when saving existing empty models.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3548 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/base.py

@@ -176,11 +176,12 @@ class Model(object):
             # If it does already exist, do an UPDATE.
             if cursor.fetchone():
                 db_values = [f.get_db_prep_save(f.pre_save(self, False)) for f in non_pks]
-                cursor.execute("UPDATE %s SET %s WHERE %s=%%s" % \
-                    (backend.quote_name(self._meta.db_table),
-                    ','.join(['%s=%%s' % backend.quote_name(f.column) for f in non_pks]),
-                    backend.quote_name(self._meta.pk.column)),
-                    db_values + [pk_val])
+                if db_values:
+                    cursor.execute("UPDATE %s SET %s WHERE %s=%%s" % \
+                        (backend.quote_name(self._meta.db_table),
+                        ','.join(['%s=%%s' % backend.quote_name(f.column) for f in non_pks]),
+                        backend.quote_name(self._meta.pk.column)),
+                        db_values + [pk_val])
             else:
                 record_exists = False
         if not pk_set or not record_exists:

tests/modeltests/empty/models.py

@@ -20,5 +20,7 @@ API_TESTS = """
 2
 >>> m.id is not None
 True
+>>> existing = Empty(m.id)
+>>> existing.save()
 
 """