Added support for distinct and db_alias (MongoEngine/mongoengine#59)

mongoengine/dereference.py

@@ -34,7 +34,9 @@ class DeReference(object):
 
         doc_type = None
         if instance and instance._fields:
-            doc_type = instance._fields[name].field
+            doc_type = instance._fields[name]
+            if hasattr(doc_type, 'field'):
+                doc_type = doc_type.field
 
             if isinstance(doc_type, ReferenceField):
                 doc_type = doc_type.document_type

mongoengine/queryset.py

@@ -1168,7 +1168,8 @@ class QuerySet(object):
         .. versionchanged:: 0.5 - Fixed handling references
         """
         from dereference import DeReference
-        return DeReference()(self._cursor.distinct(field), 1)
+        return DeReference()(self._cursor.distinct(field), 1,
+                             name=field, instance=self._document)
 
     def only(self, *fields):
         """Load only a subset of this document's fields. ::