public ResponseEntity <string> Add(Tag tag)
        {
            ResponseEntity <string> response = new ResponseEntity <string>();

            var  dao     = new TagDao(ConfigurationManager.AppSettings["mysqlConnStr"]);
            bool success = dao.AddTag(tag);

            if (success)
            {
                response = new ResponseEntity <string>(true, "添加成功", "添加成功");
            }
            else
            {
                response = new ResponseEntity <string>(true, "添加失败", "添加失败");
            }
            return(response);
        }