/// <summary>
    /// SQL命令攔(lan)截器
    /// 主要實現EF的讀寫分離
    /// </summary>
    public class SqlCommandInterceptor : DbCommandInterceptor
    {
        static SqlCommandInterceptor()
        {
            InitConfig();

            initSysTimer.Enabled = true;
            initSysTimer.Elapsed += initSysTimer_Elapsed;
            initSysTimer.Start();

            sysTimer.Enabled = true;
            sysTimer.Elapsed += sysTimer_Elapsed;
            sysTimer.Start();
        }

        private static object lockObj = new object();
        /// <summary>
        /// 定期找沒有在(zai)線的數據(ju)庫服務器
        /// </summary>
        private static Timer sysTimer = new Timer(6);
        /// <summary>
        /// 系統配置文(wen)件輪訓讀時間(jian)間(jian)隔
        /// </summary>
        private static Timer initSysTimer = new Timer(60000 * 10);
        /// <summary>
        ///　讀(du)庫，從庫集群，寫(xie)庫不用設置走默認的EF框架
        /// </summary>
        private static List<ReadDbConfig> readConnList;
        /// <summary>
        /// 配置(zhi)初始化
        /// </summary>
        private static void InitConfig()
        {
            lock (lockObj)
            {
                var temp = new List<ReadDbConfig>();
                var str = System.Configuration.ConfigurationManager.AppSettings["readDb"] ?? string.Empty;
                var readList = str.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
                if (readList != null && readList.Any())
                {
                    foreach (var item in readList)
                    {
                        var configArr = item.Split(new char[] { '|' }, StringSplitOptions.RemoveEmptyEntries);
                        temp.Add(new ReadDbConfig
                        {
                            Ip = configArr[0],
                            Port = int.Parse(configArr[1]),
                            DbName = configArr[2],
                            UserId = configArr[3],
                            Password = configArr[4],
                        });
                    }
                }
                readConnList = temp;
            }
        }
        #region Private Methods
        private static void initSysTimer_Elapsed(object sender, ElapsedEventArgs e)
        {
            InitConfig();
        }
        /// <summary>
        /// 輪詢服(fu)務(wu)
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private static void sysTimer_Elapsed(object sender, ElapsedEventArgs e)
        {
            lock (lockObj)
            {
                if (readConnList != null && readConnList.Any())
                {
                    foreach (var item in readConnList)
                    {
                        //心跳測試(shi)，將(jiang)死掉的服務(wu)器IP從列(lie)表中(zhong)移除
                        var client = new TcpClient();
                        try
                        {
                            client.Connect(new IPEndPoint(IPAddress.Parse(item.Ip), item.Port));
                        }
                        catch (SocketException)
                        {
                            //異(yi)常(chang)，沒有連接上
                            readConnList.Remove(item);
                        }
                        if (!client.Connected)
                        {
                            readConnList.Remove(item);
                        }
                    }
                }
            }
        }
        /// <summary>
        /// 處(chu)理(li)讀庫(ku)字符串
        /// </summary>
        /// <returns></returns>
        private string GetReadConn()
        {
            if (readConnList != null && readConnList.Any())
            {
                var resultConn = readConnList[Convert.ToInt32(Math.Floor((double)new Random().Next(0, readConnList.Count)))];
                return string.Format(System.Configuration.ConfigurationManager.AppSettings["readDbConnectioin"]
                    , resultConn.Ip
                    , resultConn.DbName
                    , resultConn.UserId
                    , resultConn.Password);
            }
            return string.Empty;
        }
        /// <summary>
        /// 只讀(du)庫的(de)選(xuan)擇,加工command對象
        /// </summary>
        /// <param name="command"></param>
        private void ReadDbSelect(DbCommand command)
        {
            if (!string.IsNullOrWhiteSpace(GetReadConn()))//如果配置了讀寫(xie)分離，就去(qu)實現
            {
                if (!command.CommandText.StartsWith("insert", StringComparison.InvariantCultureIgnoreCase))
                {
                    command.Connection.Close();
                    command.Connection.ConnectionString = GetReadConn();
                    command.Connection.Open();
                }
            }
        }
        #endregion

        #region Override Methods
        /// <summary>
        /// Linq to Entity生成的(de)update,delete
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void NonQueryExecuting(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
        {
            base.NonQueryExecuting(command, interceptionContext);//update,delete等寫操作直接走主庫
        }
        /// <summary>
        /// 執行sql語(yu)句，并返(fan)(fan)回第一(yi)行第一(yi)列，沒有找到返(fan)(fan)回null,如果數(shu)據(ju)庫中值(zhi)為null，則返(fan)(fan)回 DBNull.Value
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
        {
            ReadDbSelect(command);
            base.ScalarExecuting(command, interceptionContext);
        }
        /// <summary>
        /// Linq to Entity生成的(de)select,insert
        /// 發(fa)送到sqlserver之(zhi)前觸發(fa)
        /// warning:在select語句(ju)中DbCommand.Transaction為null，而ef會為每個insert添加一個DbCommand.Transaction進行包裹(guo)
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
        {
            ReadDbSelect(command);
            base.ReaderExecuted(command, interceptionContext);
        }
        /// <summary>
        /// 發送到sqlserver之后觸發
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
        {
            base.ReaderExecuted(command, interceptionContext);
        }

        #endregion
    }