tree_id expires after flushing fixes #33

sqlalchemy_mptt/events.py

@@ -408,6 +408,8 @@ def after_flush_postexec(self, session, context):
                 self.instances.discard(parent)
                 session.expire(parent, ['left', 'right'])
                 parent = self.get_parent_value(parent)
+            else:
+                session.expire(instance, ['tree_id', ])
 
     @staticmethod
     def get_parent_value(instance):

sqlalchemy_mptt/tests/tree_testing_base.py

@@ -742,7 +742,7 @@ def test_move_tree_to_another_tree(self):
 
         """
         node = self.session.query(self.model).\
-                filter(self.model.ppk == 12).one()
+            filter(self.model.ppk == 12).one()
         node.parent_id = 7
         self.session.add(node)
         #                 id lft rgt lvl parent tree
@@ -1715,3 +1715,11 @@ def test_leftsibling_in_level(self):
         self.assertEqual(node8.leftsibling_in_level().idd, node6.ppk)
         self.assertEqual(node6.leftsibling_in_level().idd, node5.ppk)
         self.assertEqual(node3.leftsibling_in_level(), None)
+
+    def test_session_expire(self):
+        """https://github.com/ITCase/sqlalchemy_mptt/issues/33"""
+        node = self.session.query(self.model).filter(self.model.ppk == 4).one()
+        node.move_after('1')
+        self.session.flush()
+        self.assertEqual(node.tree_id, 2)
+        self.assertEqual(node.parent_id, None)