带有异步Dapper方法的CancellationToken？

本文介绍了带有异步Dapper方法的CancellationToken？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在使用Nuget的Dapper 1.31。我有一个非常简单的代码段，

I'm using Dapper 1.31 from Nuget. I have this very simple code snippet,

string connString = ""; string query = ""; int val = 0; CancellationTokenSource tokenSource = new CancellationTokenSource(); using (IDbConnection conn = new SqlConnection(connString)) { conn.Open(); val = (await conn.QueryAsync<int>(query, tokenSource.Token)).FirstOrDefault(); }

当我在<$ c $上按 F12 时c> QueryAsync ，它将我指向

When I press F12 on QueryAsync, it points me to

public static Task<IEnumerable<T>> QueryAsync<T> ( this IDbConnection cnn, string sql, dynamic param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null );

签名上没有 CancellationToken 。

问题：

• 为什么代码段完全可构建假设整个解决方案没有编译器错误？
• 请原谅我无法测试是否调用 tokenSource.Cancel（）会真正取消该方法，因为我不知道如何生成长时间运行的sql查询。 .Cancel（）是否会真正取消该方法并抛出 OperationCancelledException ？

• Why is the snippet completely buildable assuming that there is no compiler error on the whole solution?
• Forgive me that I cannot test if calling tokenSource.Cancel() would really cancel the method because I don't know how to generate a long running sql query. Will the .Cancel() really cancel the method and throw OperationCancelledException?

谢谢！

推荐答案

您正在将取消令牌作为参数传递宾语;

You are passing the cancellation token as the parameter object; that won't work.

dapper中的第一个异步方法没有公开取消令牌；当我尝试将它们添加为可选参数（作为单独的重载，以避免破坏现有的程序集）时，事情与模棱两可的方法编译问题非常混淆。因此，我不得不通过单独的API公开它；输入 CommandDefinition ：

The first async methods in dapper did not expose a cancellation token; when I tried to add them as an optional parameter (as a separate overload, to avoid breaking existing assemblies), things got very confused with "ambiguous method" compilation problems. Consequently, I had to expose this via a separate API; enter CommandDefinition:

val = (await conn.QueryAsync<int>( new CommandDefinition(query, cancellationToken: tokenSource.Token) ).FirstOrDefault();

然后将取消令牌向下传递到所有预期的位置； ADO.NET提供程序的工作是实际使用，但是；它似乎在在大多数情况下，请注意，如果操作正在进行，它可能会导致 SqlException 而不是 OperationCancelledException ；取决于ADO.NET提供程序，但在很大程度上有道理：您可能已经中断了一些重要的事情；它成为一个关键的连接问题。

This then passes the cancellation-token down the chain to all the expected places; it is the job of the ADO.NET provider to actually use it, but; it seems to work in most cases. Note that it can result in a SqlException rather than an OperationCancelledException if the operation is in progress; this again is down to the ADO.NET provider, but makes a lot of sense: you could have interrupted something important; it surfaces as a critical connection issue.

对于这些问题：

假设整个解决方案都没有编译器错误，为什么该代码段是完全可构建的？

Why is the snippet completely buildable assuming that there is no compiler error on the whole solution?

因为...它是有效的C＃，即使它不是d

Because... it is valid C#, even if it doesn't do what you expect.

请原谅我，因为我无法测试调用tokenSource.Cancel（）是否真的取消了该方法，因为我没有知道如何生成长时间运行的sql查询。 .Cancel（）会真正取消该方法并引发OperationCancelledException吗？

Forgive me as I cannot test if calling tokenSource.Cancel() would really cancel the method because I don't know how to generate long running sql query. Will the .Cancel() really cancels the method and throws OperationCancelledException?

ADO.NET提供程序特定的，但可以正常使用。作为如何生成长时间运行的SQL查询的示例； SQL Server上的 waitfor delay 命令在这里有些有用，这也是我在集成测试中使用的。

ADO.NET provider-specific, but yes it usually works. As an example of "how to generate long running sql query"; the waitfor delay command on SQL server is somewhat useful here, and is what I use in the integration tests.