Fix derefcence failed some case.

mongoengine/dereference.py

@@ -1,7 +1,7 @@
 import pymongo
 
 from base import (BaseDict, BaseList, TopLevelDocumentMetaclass, get_document)
-from fields import ReferenceField
+from fields import (ReferenceField, ListField, DictField, MapField)
 from connection import get_db
 from queryset import QuerySet
 from document import Document
@@ -102,7 +102,7 @@ class DeReference(object):
                 for key, doc in references.iteritems():
                     object_map[key] = doc
             else:  # Generic reference: use the refs data to convert to document
-                if doc_type:
+                if doc_type and not isinstance(doc_type, (ListField, DictField, MapField,) ):
                     references = doc_type._get_db()[col].find({'_id': {'$in': refs}})
                     for ref in references:
                         doc = doc_type._from_son(ref)