public MessageModel <string> Post([FromBody] MngAdmin model)
 {
     MngAdminService.AddEntity(model);
     return(new MessageModel <string>
     {
         success = true,
         msg = "添加成功"
     });
 }
        public MessageModel <MngAdmin> Get(int id)
        {
            MngAdmin model = MngAdminService.FindSingle(f => f.Id == id);
            bool     flag  = model != null || model.Id > 0;

            return(new MessageModel <MngAdmin>
            {
                success = flag,
                msg = flag ? "查询成功" : $"没有id为{id}的数据",
                model = flag ? model : new MngAdmin()
            });
        }