Fix derefcence failed some case.

tests/dereference.py

@@ -783,3 +783,41 @@ class FieldTest(unittest.TestCase):
         root = root.reload()
         self.assertEquals(root.children, [company])
         self.assertEquals(company.parents, [root])
+    
+    def test_dict_in_dbref_instance(self):
+
+        class Person(Document):
+            name = StringField(max_length=250, required=True)
+
+            meta = { "ordering" : "name" }
+        
+        class Room(Document):
+            number = StringField(max_length=250, required=True)
+            staffs_with_position = ListField(DictField())
+
+            meta = { "ordering" : "number" }
+
+
+
+        Person.drop_collection()
+
+        # 201
+        bob = Person.objects.create(name='Bob')
+        bob.save()
+        keven = Person.objects.create(name='Keven')
+        keven.save()
+        sarah = Person.objects.create(name='Sarah')
+        sarah.save()
+
+        room_201 = Room.objects.create( number = "201")
+        room_201.staffs_with_position = [ {'position_key': 'window', 'staff' : sarah.to_dbref() },
+                                         { 'position_key': 'door', 'staff': bob.to_dbref() },
+                                         { 'position_key': 'center' , 'staff' : keven.to_dbref() } ]
+        room_201.save()
+
+        room = Room.objects.first().select_related()
+        room.to_mongo()
+
+
+
+