///
///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}
)
