如何理解transaction.complete函数？

Question

大家好，我们已经开始使用事务范围，下面是代码 sn-p。我们需要了解的是基于我们在每次使用连接后的理解，特定连接将被释放/关闭对吗？那么自从它关闭后，transaction.complete 是如何工作的呢？

using (TransactionScope transScope = new TransactionScope())
{
   try
   {
      string myConnStringLocal = "User Id=***;Password=****;Host=" + globalSettings.settingLocalIP + ";Database=" + globalSettings.settingLocalDB;
      using (MySqlConnection connectionLocal = new MySqlConnection(myConnStringLocal))
      {
         try{
         connectionLocal.Open();
         }
         Catch(Exception e)
         {

         }
         finally{
         connectionLocal.Close();
         }
      }

      string myConnStringCentral = "User Id=***;Password=*****;Host=" + globalSettings.settingCentralIP + ";Database=" + globalSettings.settingCentralDB;
      using (MySqlConnection connectionCentral = new MySqlConnection(myConnStringCentral))
      {
         try{
         connectionCentral.Open();
         }
         Catch(Exception e)
         {

         }
         finally{
         connectionCentral.Close();
         }

      }
      string myConnStringCentralCopy = "User Id=*****;Password=*****;Host=" + globalSettings.settingCentralCopyIP + ";Database=" + globalSettings.settingCentralCopyDB;
      using (MySqlConnection connectionCentralCopy = new MySqlConnection(myConnStringCentralCopy))
      {
         try{
         connectionCentralCopy.Open();
         }
         Catch(Exception e)
         {

         }
         finally{
         connectionCentralCopy.Close();
         }
      }
      transScope.Complete();
      Console.WriteLine("Transaction is completed");
   }
   catch (Exception)
   {
      Console.WriteLine("Transaction is rolled back");
   }
}

Answer 1

TransactionScope.Complete 告诉所有事务管理器他们可以提交这个事务。这并不能保证一切都会实际提交。在调用 Complete 方法后，所有事务管理器都单独启动提交，如果所有事务管理器都成功，则认为事务成功完成。 你可以参考这个link for further details

Answer 2

当您在单个TransactionScope 中连接到多个数据库时，事务将升级为distributed 事务并由MSDTC 使用2-phase commit 进行协调。

关于连接关闭 - 这是在 TransactionScope 内关闭连接时的特殊情况，在内部它由 System.Transactions 基础设施管理，因此即使连接从您端关闭，数据库会话仍可能打开。

在MSDN上查看此注释：

如果启用了连接池，则在重置连接时会自动回滚使用 Transact-SQL 或 BeginTransaction 启动的待处理事务。如果连接池关闭，则在调用 SqlConnection.Close 后回滚事务。通过 System.Transactions 启动的事务通过 System.Transactions 基础结构进行控制，不受 SqlConnection.Close 影响

编辑根据您的 cmets，您可以执行以下操作：

try
{
   using (TransactionScope transScope = new TransactionScope())
   {
      string myConnStringLocal = ...;
      using (var connectionLocal = new MySqlConnection(myConnStringLocal))
      {
         connectionLocal.Open();
         // do your DB update 

      } //no need to close connection explicitly, the using() {..} statement does that for you

      string myConnStringCentral = ...;
      using (var connectionCentral = new MySqlConnection(myConnStringCentral))
      {
         connectionCentral.Open();
         // do your DB update

      } //no need to close connection explicitly, the using() {..} statement does that for you

      string myConnStringCentralCopy = ...;
      using (var connectionCentralCopy = new MySqlConnection(myConnStringCentralCopy))
      {         
         connectionCentralCopy.Open();
         // do your DB update

      } //no need to close connection explicitly, the using() {..} statement does that for you

      transScope.Complete();

      Console.WriteLine("Transaction is completed");

   } //no need to dispose transactionScope explicitly, the using() {..} statement does that for you
}
catch (Exception)
{
      // If any exception occurs in the try block above transScope.Complete() line will be caught here
      // and will automatically cause the transaction to rollback.
      Console.WriteLine("Transaction is rolled back");
}

// You can then start new TransactionScope if you want to further update more than one DB in a transactional manner.
try
{
   using (TransactionScope transScope = new TransactionScope())
   {
      //...

   }
}
catch (Exception)
{
     //...
}

Answer 3

当调用Complete 方法时，如果没有抛出Exception，则范围内的所有内容都将被提交。如果代码在没有Complete 的情况下超出范围，则不会发生提交。简而言之，如果您调用Complete 方法，那么，如果没有Exceptions 抛出，您在给定TransactionScope 范围内的事务将被提交。

另外，我必须补充一点，可能还有一个层次结构，TransactionScopes 的树。您还可以为TransactionScope 的子范围回滚的情况设置TransactionScope 的行为。