交易目的

Question

我读了很多关于这个主题的文章，我仍然有一些重要的基本问题。 如果它不用于SQL，那么事务的目的是什么？它对wcf有什么帮助？ 本文展示了使用简单事务的示例：

http://msdn.microsoft.com/en-us/library/ms172152(v=vs.90).aspx

下面这段代码的目的是什么，如果它不是为了回滚他们试图恢复的代码，以防代码失败？

    void RootMethod()
{
     using(TransactionScope scope = new TransactionScope())
     {
          /* Perform transactional work here */
          SomeMethod();
          scope.Complete();
     }
}

void SomeMethod()
{
     using(TransactionScope scope = new TransactionScope())
     {
          /* Perform transactional work here */
          scope.Complete();
     }
}

Answer 1

只有支持交易的资源才能参与交易。通常，这只是SQL Server。消息队列还支持事务。

如果您不使用任何启用事务的资源（如正常变量...），则无法执行任何操作。

Answer 2

这里有一个很好的例子

http://msdn.microsoft.com/en-us/library/system.transactions.transactionscope(v=vs.90).aspx#Y500

在示例（上面的链接，下面的代码）中，SQL连接对象将自动参与事务 - 因此这些SQL命令在事务完成之前不会提交（scope.Complete）。这样，只有当另一个服务器发生时，两个服务器才会发生。任何异常都会导致两者都回滚。

您的示例不明确，因为它仅在该页面的上下文中描述嵌套作用域。这个例子显示了一些被认为是嵌套的东西，而不是一些可以做任何有用的代码。

这是微软的示例代码，我认为非常清楚：

// This function takes arguments for 2 connection strings and commands to create a transaction 
// involving two SQL Servers. It returns a value > 0 if the transaction is committed, 0 if the 
// transaction is rolled back. To test this code, you can connect to two different databases 
// on the same server by altering the connection string, or to another 3rd party RDBMS by 
// altering the code in the connection2 code block.
static public int CreateTransactionScope(
    string connectString1, string connectString2,
    string commandText1, string commandText2)
{
    // Initialize the return value to zero and create a StringWriter to display results.
    int returnValue = 0;
    System.IO.StringWriter writer = new System.IO.StringWriter();

    try
    {
        // Create the TransactionScope to execute the commands, guaranteeing
        // that both commands can commit or roll back as a single unit of work.
        using (TransactionScope scope = new TransactionScope())
        {
            using (SqlConnection connection1 = new SqlConnection(connectString1))
            {
                // Opening the connection automatically enlists it in the 
                // TransactionScope as a lightweight transaction.
                connection1.Open();

                // Create the SqlCommand object and execute the first command.
                SqlCommand command1 = new SqlCommand(commandText1, connection1);
                returnValue = command1.ExecuteNonQuery();
                writer.WriteLine("Rows to be affected by command1: {0}", returnValue);

                // If you get here, this means that command1 succeeded. By nesting
                // the using block for connection2 inside that of connection1, you
                // conserve server and network resources as connection2 is opened
                // only when there is a chance that the transaction can commit.   
                using (SqlConnection connection2 = new SqlConnection(connectString2))
                {
                    // The transaction is escalated to a full distributed
                    // transaction when connection2 is opened.
                    connection2.Open();

                    // Execute the second command in the second database.
                    returnValue = 0;
                    SqlCommand command2 = new SqlCommand(commandText2, connection2);
                    returnValue = command2.ExecuteNonQuery();
                    writer.WriteLine("Rows to be affected by command2: {0}", returnValue);
                }
            }

            // The Complete method commits the transaction. If an exception has been thrown,
            // Complete is not  called and the transaction is rolled back.
            scope.Complete();

        }

    }
    catch (TransactionAbortedException ex)
    {
        writer.WriteLine("TransactionAbortedException Message: {0}", ex.Message);
    }
    catch (ApplicationException ex)
    {
        writer.WriteLine("ApplicationException Message: {0}", ex.Message);
    }

    // Display messages.
    Console.WriteLine(writer.ToString());

    return returnValue;
}