From 3b4df4615add363febff12c814529633ca0d70d4 Mon Sep 17 00:00:00 2001
From: Harry Marr <harry.marr@gmail.com>
Date: Sat, 17 Apr 2010 21:45:11 +0100
Subject: [PATCH] Fixed MRO error that occured on document inheritance

---
 mongoengine/base.py | 21 +++++++++++----------
 tests/document.py   |  5 +++++
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/mongoengine/base.py b/mongoengine/base.py
index bd3f11ad..83faa92e 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -187,19 +187,20 @@ class DocumentMetaclass(type):
         for field in new_class._fields.values():
             field.owner_document = new_class
 
-        module = attrs.pop('__module__')
+        module = attrs.get('__module__')
         
-        new_class.add_to_class('DoesNotExist', subclass_exception('DoesNotExist',
-                            tuple(x.DoesNotExist
-                                  for k,x in superclasses.items())
-                            or (DoesNotExist,), module))
+        base_excs = tuple(base.DoesNotExist for base in bases 
+                          if hasattr(base, 'DoesNotExist')) or (DoesNotExist,)
+        exc = subclass_exception('DoesNotExist', base_excs, module)
+        new_class.add_to_class('DoesNotExist', exc)
         
-        new_class.add_to_class('MultipleObjectsReturned', subclass_exception('MultipleObjectsReturned',
-                            tuple(x.MultipleObjectsReturned
-                                  for k,x in superclasses.items())
-                            or (MultipleObjectsReturned,), module))
-        return new_class
+        base_excs = tuple(base.MultipleObjectsReturned for base in bases 
+                          if hasattr(base, 'MultipleObjectsReturned'))
+        base_excs = base_excs or (MultipleObjectsReturned,)
+        exc = subclass_exception('MultipleObjectsReturned', base_excs, module)
+        new_class.add_to_class('MultipleObjectsReturned', exc)
     
+        return new_class
         
     def add_to_class(self, name, value):
         setattr(self, name, value)
diff --git a/tests/document.py b/tests/document.py
index a17aebdc..a753fa71 100644
--- a/tests/document.py
+++ b/tests/document.py
@@ -127,6 +127,11 @@ class DocumentTest(unittest.TestCase):
         self.assertEqual(Employee._meta['collection'], 
                          self.Person._meta['collection'])
 
+        # Ensure that MRO error is not raised
+        class A(Document): pass
+        class B(A): pass
+        class C(B): pass
+
     def test_allow_inheritance(self):
         """Ensure that inheritance may be disabled on simple classes and that
         _cls and _types will not be used.