diff --git a/chapter_4/answer/DataBaseManager.py b/chapter_4/answer/DataBaseManager.py
index 3d42135..634f313 100755
--- a/chapter_4/answer/DataBaseManager.py
+++ b/chapter_4/answer/DataBaseManager.py
@@ -29,7 +29,7 @@ def _query_last_id(self):
         :return: 最新ID
         """
         last_info = self.handler.find({}, {'_id': 0, 'id': 1}).sort('id', -1).limit(1)
-        return last_info[0]['id'] if last_info else 0
+        return last_info[0]['id'] if last_info.count() else 0
 
     def add_info(self, para_dict):
         """