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C#事务异常TransactionScope Troubleshooting

只要涉及到数据库的操作,那么使用事务就是难免的。如果我们使用LINQ to SQL作为数据访问层,那么LINQ提供的SubmitChanges()方法自身就包含了对事务的处理。当然,我们也可以利用System.Data.Common.DbTransaction对事务进行处理,我们可以调用DataContext中Connection的方法BeginTransaction()启动事务,然后根据情况进行回滚或提交。例如是这样一段代码:

LinqSampleDataContext context = new LinqSampleDataContext();                 System.Data.Common.DbTransaction trans = null;     try    {        context.Connection.Open();        trans = context.Connection.BeginTransaction();        context.Transaction = trans;            context.Employees.InsertOnSubmit(emp);                     context.SubmitChanges();            trans.Commit();     }     catch (Exception ex)     {        if (trans != null)        {            trans.Rollback();        }     }

然而,当我们在使用LINQ to SQL中时,往往会同时使用多个DataContext,此时我们就需要使用TransactionScope。例如:

using (TransactionScope scope = new TransactionScope(TransactionScopeOption.RequiresNew))     {         try        {               for (int i = 0; i < nominees.Count; ++i)             {                 Backup newBackup = nominees[i];                 Ticket ticket = tickets[i];                   //update the information of ticket                 //mainly add the information of employee;                 ticket.EmployeeID = newBackup.EmployeeID;                 ticket.HaveNominated = true;                 ticket.IsConfirmedByManager = true;                 ticket.Status = TicketStatus.Enroll.ToString();                   ticketAccessor.Update(ticket);             }               //update the IsSubmit of backup;             ChangeSubmitStatue(backup);               //remove the record of nominee in backup table             Delete(nominees);         }         catch (Exception ex)         {             ThrowHelper.ThrowBackupException("Finalizing occurs an error. The transcation will be rollback.");             return false;         }           scope.Complete();     }

 

代码中,分别涉及到Update, Delete等操作,因此我们势必需要用事务,保证数据整体提交或整体回滚。在使用事务的时候,有一些前置条件是必备的。例如启动Distributed Transaction Coordinator服务,否则,就会抛出System.Data.SqlClient.SqlException异常,信息为:”MSDTC on server ‘{Server Name}’ is unavailable.”。是的,很多资料都是这样描述的。然而,现实并没有这么简单。我们首先得考虑运行代码的机器是否与数据库所在的机器是同一台。这里所谓的启动Distributed Transaction Coordinator服务,实际上是要启动数据库服务器的服务。如果数据库与代码服务器是同一台,通过这样的设置就没有错误了。
当数据库与代码服务器分属两台机器呢?同样运行如上的代码,就会抛出System.Transactions.TransactionManagerCommunicationException异常。异常信息为:”Network access for Distributed Transaction Manager (MSDTC) has been disabled. Please enable DTC for network access in the security configuration for MSDTC using the Component Services Administrative tool.”
这是一种通信错误,原因在于两台服务器之间的安全配置禁止了分布式事务。解决办法是在运行代码的服务器上,配置Component Services。方法如下:
1、在Run运行窗口中,输入dcomcnfg命令,这样就可以打开Component Services。
2、选择Component Services->Computers->My Computer;
3、右键单击My Computer,在弹出的快捷菜单中,选择“Properties”,然后点击MSDTC tab;
4、在MSDTC tab中,点击Security Configuration按钮;
5、在弹出的对话框中参照下表的建议进行设置:

 

 

Configuration Option Default Value Recommended Value
Network DTC Access Disabled Enabled
Client and Administration
Allow Remote Clients Disabled Disabled
Allow Remote Administration Disabled Disabled
Transaction Manager Communication
Allow Inbound Disabled Enabled
Allow Outbound Disabled Enabled
Mutual Authentication Required Enabled Enabled if all remote machines are running Win2K3 SP1 or XP SP2 or higher, and are configured with “Mutual Authentication Required”.
Incoming Caller Authentication Required Disabled Enabled if running MSDTC on cluster.
No Authentication Required Disabled Enabled if remote machines are pre-Windows Server 2003 SP1 or pre- Windows XP SP2.
Enable TIP Disabled Enabled if running the BAM Portal.
Enable XA Transactions Disabled Enabled if communicating with an XA based transactional system such as when communicating with IBM WebSphere MQ using the MQSeries adapter.

最后的设置如截图:

如果操作系统是Windows 2003,通常默认的设置就是正确的。不过我们在编写程序时,不管是Unit Test,还是其他测试,最频繁的还是在本机上运行。如果操作系统是Windows XP,就不得不进行这样的设置了。

注: 此贴中没写在防火墙中加入msdtc.exe,值得商榷

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