fix get_tree with emty table.

CHANGES.rst

@@ -1,3 +1,8 @@
+0.1.6 (2015-07-03)
+==================
+
+- fix bug with ``get_tree`` when no rows in database.
+
 0.1.5 (2015-06-25)
 ==================
 
@@ -62,47 +67,3 @@ Bug Fixes
 
 - Fix concurrency issue with multiple session (#36)
 - Flushing the session now expire the instance and it's children (#33)
-
-0.0.9 (2014-10-09)
-==================
-
-- Add MANIFEST.in
-- New docs
-- fixes in setup.py
-
-0.0.8 (2014-08-15)
-==================
-
-- Add CONTRIBUTORS.txt
-
-Features
---------
-
-- Automatically register tree classes enhancement (#28)
-- Added support polymorphic tree models (#24)
-
-Bug Fixes
----------
-
-- Fix expire left/right attributes of parent somewhen after the `before_insert` event (#30)
-- Fix tree_id is incorrectly set to an existing tree if no parent is set (#23)
-- Fix package is not installable if sqlalchemy is not (yet) installed (#22)
-
-0.0.7 (2014-08-04)
-==================
-
-- Add LICENSE.txt
-
-Bug Fixes
----------
-
-- fix get_db_pk function
-
-
-0.0.6 (2014-07-31)
-==================
-
-Bug Fixes
----------
-
--  Allow the primary key to not be named "id" #20. See https://github.com/ITCase/sqlalchemy_mptt/issues/20

CHANGES_OLD.rst

@@ -0,0 +1,43 @@
+0.0.9 (2014-10-09)
+==================
+
+- Add MANIFEST.in
+- New docs
+- fixes in setup.py
+
+0.0.8 (2014-08-15)
+==================
+
+- Add CONTRIBUTORS.txt
+
+Features
+--------
+
+- Automatically register tree classes enhancement (#28)
+- Added support polymorphic tree models (#24)
+
+Bug Fixes
+---------
+
+- Fix expire left/right attributes of parent somewhen after the `before_insert` event (#30)
+- Fix tree_id is incorrectly set to an existing tree if no parent is set (#23)
+- Fix package is not installable if sqlalchemy is not (yet) installed (#22)
+
+0.0.7 (2014-08-04)
+==================
+
+- Add LICENSE.txt
+
+Bug Fixes
+---------
+
+- fix get_db_pk function
+
+
+0.0.6 (2014-07-31)
+==================
+
+Bug Fixes
+---------
+
+-  Allow the primary key to not be named "id" #20. See https://github.com/ITCase/sqlalchemy_mptt/issues/20

sqlalchemy_mptt/__init__.py

@@ -10,7 +10,7 @@
 from .mixins import BaseNestedSets
 from .events import TreesManager
 
-__version__ = "0.1.6.dev1"
+__version__ = "0.1.6"
 __mixins__ = [BaseNestedSets]
 __all__ = ['BaseNestedSets', 'mptt_sessionmaker']
 

sqlalchemy_mptt/mixins.py

@@ -209,7 +209,7 @@ def query(nodes):
         nodes = nodes.order_by(cls.tree_id, cls.level, cls.left).all()
 
         # search minimal level of nodes.
-        min_level = min([node.level for node in nodes])
+        min_level = min([node.level for node in nodes] or [None])
 
         def get_node_id(node):
             return getattr(node, node.get_pk_name())

sqlalchemy_mptt/tests/cases/get_tree.py

@@ -4,6 +4,23 @@ def get_obj(session, model, id):
 
 class Tree(object):
 
+    def test_get_empty_tree(self):
+        """
+            No rows in database.
+        """
+        self.session.query(self.model).delete()
+        self.session.flush()
+        tree = self.model.get_tree(self.session)
+        self.assertEqual(tree, [])
+
+    def test_get_empty_tree_with_custom_query(self):
+        """
+            No rows with id < 0.
+        """
+        query = lambda x: x.filter(self.model.get_pk_column() < 0)
+        tree = self.model.get_tree(self.session, query=query)
+        self.assertEqual(tree, [])
+
     def test_get_tree(self):
         """.. note::