add _drilldown_query method

setup.py

@@ -10,7 +10,7 @@ def read(name):
 
 setup(
     name='sqlalchemy_mptt',
-    version='0.1.7',
+    version='0.1.8.dev1',
     url='http://github.com/ITCase/sqlalchemy_mptt/',
     author='Svintsov Dmitry',
     author_email='[email protected]',

sqlalchemy_mptt/mixins.py

@@ -243,6 +243,12 @@ def get_node_id(node):
                 nodes_of_level[get_node_id(node)] = tree[-1]
         return tree
 
+    def _drilldown_query(self, nodes):
+        table = self.__class__
+        return nodes.filter(table.tree_id == self.tree_id)\
+            .filter(table.left >= self.left)\
+            .filter(table.right <= self.right)
+
     def drilldown_tree(self, session=None, json=False, json_fields=None):
         """ This method generate a branch from a tree, begining with current
         node.
@@ -269,13 +275,8 @@ def drilldown_tree(self, session=None, json=False, json_fields=None):
 
             * :mod:`sqlalchemy_mptt.tests.cases.get_tree.test_drilldown_tree`
         """
-        def query(nodes):
-            table = self.__class__
-            return nodes.filter(table.tree_id == self.tree_id)\
-                .filter(table.left >= self.left)\
-                .filter(table.right <= self.right)
         return self.get_tree(session, json=json, json_fields=json_fields,
-                             query=query)
+                             query=self._drilldown_query)
 
     def path_to_root(self, session=None):
         """Generate path from a leaf or intermediate node to the root.