From c081aca79431e7e060e66c2e4d4da88cc66ed8ae Mon Sep 17 00:00:00 2001
From: Karim Allah <karimallah@KarimAllah-desktop.(none)>
Date: Sun, 25 Sep 2011 18:58:40 +0200
Subject: [PATCH] Fixing dereferencing when the dereferenced-document wasn't
 found.

---
 mongoengine/base.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mongoengine/base.py b/mongoengine/base.py
index 92a5b71a..d02848f1 100644
--- a/mongoengine/base.py
+++ b/mongoengine/base.py
@@ -10,6 +10,7 @@ import pymongo
 import pymongo.objectid
 import operator
 from functools import partial
+from bson.dbref import DBRef
 
 
 class NotRegistered(Exception):
@@ -97,6 +98,9 @@ class BaseField(object):
 
         # Get value from document instance if available, if not use default
         value = instance._data.get(self.name)
+	if isinstance(value, DBRef):
+		raise ValueError("Can't dereference from the given DBRef (%s)" % str(value))
+
         if value is None:
             value = self.default
             # Allow callable default values