EF架構~通過EF6的DbCommand攔截器來實現數據庫讀寫分離~續~添加事務機制

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上一講中簡單介紹了一個EF環境下通過DbCommand攔截器來實現SQLSERVER的讀寫分離，只是一個最簡單的實現，而如果出現事務情況，還是會有一些問題的，因為在攔截器中我們手動開啟了Connection鏈接，而在一個ＷＥＢ請求時，如果你的一個變量即用到了read庫又用到了write庫，就會導致到sqlserver端的spid（system process id，系統進程ＩＤ，sqlserver里可能是某個數據庫進程序的ＩＤ）發生變化　，而對於這種變化，原本是本地的事務就會自動提升為分布式事務，對MSDTC不了解的同學，可能看我的相關文章，所以，我們使用攔截實現讀寫分離后，在程序里，你的讀和寫的倉儲對象要分別定義，不能共享，而且，你在事務里所以寫的倉儲對象都要使用同一個數據上下文！

當你按着我說的做后，本地事務就不會提升為msdtc了，如圖：

今天我在DbCommand攔截器進行了優化，下面共享一下代碼，如是測試不是真實一項目代碼

    /// <summary>
    /// SQL命令攔截器
    /// </summary>
    public class SqlCommandInterceptor : DbCommandInterceptor
    {
        /// <summary>
        ///　讀庫，從庫集群，寫庫不用設置走默認的EF框架
        /// </summary>
        string readConn = System.Configuration.ConfigurationManager.AppSettings["readDb"] ?? string.Empty;
        private string GetReadConn()
        {
            var readArr = readConn.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
            var resultConn = string.Empty;
            if (readArr != null && readArr.Any())
            {
                resultConn = readArr[Convert.ToInt32(Math.Floor((double)new Random().Next(0, readArr.Length)))];
            }
            return resultConn;
        }
        //linq to entity生成的update,delete
        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語句，並返回第一行第一列，沒有找到返回null,如果數據庫中值為null，則返回 DBNull.Value
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void ScalarExecuting(DbCommand command,
           DbCommandInterceptionContext<object> interceptionContext)
        {
            if (!string.IsNullOrWhiteSpace(GetReadConn()))//如果配置了讀寫分離，就去實現
            {
                if (!command.CommandText.StartsWith("insert", StringComparison.InvariantCultureIgnoreCase))
                {
                    command.Connection.Close();
                    command.Connection.ConnectionString = GetReadConn();
                    command.Connection.Open();
                }
            }
            base.ScalarExecuting(command, interceptionContext);
        }

        /// <summary>
        /// linq to entity生成的select,insert
        /// 發送到sqlserver之前觸發
        /// warning:在select語句中DbCommand.Transaction為null，而ef會為每個insert添加一個DbCommand.Transaction進行包裹
        /// </summary>
        /// <param name="command"></param>
        /// <param name="interceptionContext"></param>
        public override void ReaderExecuting(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
        {
            if (!string.IsNullOrWhiteSpace(GetReadConn()))//如果配置了讀寫分離，就去實現
            {
                if (!command.CommandText.StartsWith("insert", StringComparison.InvariantCultureIgnoreCase))
                {
                    command.Connection.Close();
                    command.Connection.ConnectionString = GetReadConn();
                    command.Connection.Open();
                }
            }
            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);
        }
    }

運行程序可以設置一些測試代碼

 public ActionResult Index()
        {
            IUnitOfWork db = new backgroundEntities();
            IRepository<WebManageUsers> readUser = new BackgroundRepositoryBase<WebManageUsers>();
            var a = readUser.GetModel().ToList();//讀庫
            using (var trans = new TransactionScope())//事務寫庫
            {
                IRepository<WebManageUsers> userWrite = new BackgroundRepositoryBase<WebManageUsers>(db);
                IRepository<WebManageMenus> menuWrite = new BackgroundRepositoryBase<WebManageMenus>(db);
                var entity = new WebManageUsers
              {
                  WebSystemID = 0,
                  CreateDate = DateTime.Now,
                  DepartmentID = 3,
                  Description = "",
                  Email = "",
                  LoginName = "test",
                  Mobile = "",
                  Operator = "",
                  Password = "",
                  RealName = "test",
                  Status = 1,
                  UpdateDate = DateTime.Now,
              };
                var entity2 = new WebManageMenus
               {
                   ParentID = 1,
                   About = "",
                   LinkUrl = "",
                   MenuLevel = 1,
                   MenuName = "test",
                   Operator = "",
                   SortNumber = 1,
                   Status = 1,
                   UpdateDate = DateTime.Now,
               };
                userWrite.Insert(entity);
                menuWrite.Insert(entity2);
                trans.Complete();
            }



            return View(a);
        }

最后的結果就是我們想要的，這里說明一點，倉儲大步的讀寫分離沒有數據庫壓力這塊的考慮，只是隨機去訪問某個讀庫。

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