///

///SQL命令拦截器///主要实现EF的读写分离///

public classCommandInterceptor : DbCommandInterceptor

{staticCommandInterceptor()

{

readConnList=DistributedReadWriteManager.Instance;

sysTimer.Enabled= true;

sysTimer.Elapsed+=sysTimer_Elapsed;

sysTimer.Start();

}///

///是否在一个事务中，如果是select,insert,update,delete都走主库///ThreadStatic标识它只在当前线程有效///

[ThreadStatic]public static bool IsTransactionScope = false;///

///锁住它///

private static object lockObj = new object();///

///定期找没有在线的数据库服务器///

private static Timer sysTimer = new Timer(5000);///

///读库，从库集群，写库不用设置走默认的EF框架///

private static IListreadConnList;#region Private Methods

private static void sysTimer_Elapsed(objectsender, ElapsedEventArgs e)

{if (readConnList != null &&readConnList.Any())

{foreach (var item inreadConnList)

{//心跳测试，将死掉的服务器IP从列表中移除

var client = newTcpClient();try{

client.Connect(newIPEndPoint(IPAddress.Parse(item.Ip), item.Port));

}catch(SocketException)

{//异常，没有连接上

readConnList.Remove(item);

}if (!client.Connected)

{

readConnList.Remove(item);

}

}

}

}///

///处理读库字符串///

///

private stringGetReadConn()

{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["readDbConnection"]

, resultConn.Ip

, resultConn.DbName

, resultConn.UserId

, resultConn.Password);

}return string.Empty;

}///

///只读库的选择,加工command对象///说明：事务中,所有语句都走主库，事务外select走读库,insert,update,delete走主库///希望：一个ＷＥＢ请求中，读与写的仓储使用一个，不需要在程序中去重新定义///

///

private voidReadDbSelect(DbCommand command)

{if (!string.IsNullOrWhiteSpace(GetReadConn()))//如果配置了读写分离，就去实现

{

command.Connection.Close();if (!command.CommandText.StartsWith("insert", StringComparison.InvariantCultureIgnoreCase) && !IsTransactionScope)

command.Connection.ConnectionString=GetReadConn();

command.Connection.Open();

}

}#endregion

#region Override Methods

///

///Linq to Entity生成的update,delete///

///

///

public override void NonQueryExecuting(DbCommand command, DbCommandInterceptionContextinterceptionContext)

{base.NonQueryExecuting(command, interceptionContext);//update,delete等写操作直接走主库

}///

///执行sql语句，并返回第一行第一列，没有找到返回null,如果数据库中值为null，则返回 DBNull.Value///

///

///

public override void ScalarExecuting(DbCommand command, DbCommandInterceptionContextinterceptionContext)

{

ReadDbSelect(command);base.ScalarExecuting(command, interceptionContext);

}///

///Linq to Entity生成的select,insert///发送到sqlserver之前触发///warning:在select语句中DbCommand.Transaction为null，而ef会为每个insert添加一个DbCommand.Transaction进行包裹///

///

///

public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContextinterceptionContext)

{

ReadDbSelect(command);base.ReaderExecuted(command, interceptionContext);

}///

///发送到sqlserver之后触发///

///

///

public override void ReaderExecuted(DbCommand command, DbCommandInterceptionContextinterceptionContext)

{base.ReaderExecuted(command, interceptionContext);

}#endregion}