c# - ASP.NET MVC2 从 jQuery 调用 AsyncController 方法？

Question

我正在尝试学习如何在 MVC2 中使用 AsyncController，但那里的文档/教程很少。我希望采用一种普通的 Controller 方法，该方法导出到第 3 方服务的速度非常慢，并将其转换为异步方法。

原来的 Controller 方法:

public JsonResult SaveSalesInvoice(SalesInvoice invoice)
{
    SaveInvoiceToDatabase(invoice); // this is very quick 
    ExportTo3rdParty(invoice); // this is very slow and should be async
}

所以我创建了一个继承自 AsyncController 的新 Controller :

public class BackgroundController : AsyncController
{
    public void ExportAysnc(int id)
    {
        SalesInvoice invoice = _salesService.GetById(id);
        ExportTo3rdParty(invoice);
    }

    public void ExportCompleted(int id)
    {
         // I dont care about the return value right now, 
         // because the ExportTo3rdParty() method
         // logs the result to a table
    }

    public void Hello(int id)
    {            
    }
}

然后从 jQuery 中调用 Export 方法:

function Export() {
    $.post("Background/Export", { id: $("#Id").val() }, function (data) {
    // nothing to do yet
    });
}

但结果是 404 未找到错误(未找到后台/导出)。如果我尝试调用 Background/Hello 或 Background/ExportAysnc，就会找到它们。

我做错了什么？

Answer 1

确实有两个用例

1. 您关心长时间操作的结果
2. 你不关心结果(即发即弃)

让我们从第一个案例开始:

public class BackgroundController : AsyncController
{
    public void ExportAysnc(int id)
    {
        AsyncManager.OutstandingOperations.Increment();

        Task.Factory.StartNew(() => DoLengthyOperation(id));

        // Remark: if you don't use .NET 4.0 and the TPL 
        // you could manually start a new thread to do the job
    }

    public ActionResult ExportCompleted(SomeResult result)
    {
        return Json(result, JsonRequestBehavior.AllowGet);
    }

    private void DoLengthyOperation(int id)
    {
        // TODO: Make sure you handle exceptions here
        // and ensure that you always call the AsyncManager.OutstandingOperations.Decrement()
        // method at the end
        SalesInvoice invoice = _salesService.GetById(id);
        AsyncManager.Parameters["result"] = ExportTo3rdParty(invoice);
        AsyncManager.OutstandingOperations.Decrement();
    }
}

现在你可以像这样调用它:

$.getJSON(
    '<%= Url.Action("Export", "Background") %>', 
    { id: $("#Id").val() }, 
    function (data) {
        // do something with the results
    }
);

现在因为您提到了 Web 服务调用，这意味着当您生成 Web 服务的客户端代理时，您有机会发出异步方法(XXXCompleted 和 XXXAsync):

public class BackgroundController : AsyncController
{
    public void ExportAysnc(int id)
    {
        AsyncManager.OutstandingOperations.Increment();
        // that's the web service client proxy that should
        // contain the async versions of the methods
        var someService = new SomeService();
        someService.ExportTo3rdPartyCompleted += (sender, e) =>
        {
            // TODO: Make sure you handle exceptions here
            // and ensure that you always call the AsyncManager.OutstandingOperations.Decrement()
            // method at the end

            AsyncManager.Parameters["result"] = e.Value;
            AsyncManager.OutstandingOperations.Decrement();
        };
        var invoice = _salesService.GetById(id);
        someService.ExportTo3rdPartyAsync(invoice);
    }

    public ActionResult ExportCompleted(SomeResult result)
    {
        return Json(result, JsonRequestBehavior.AllowGet);
    }
}

这是异步 Controller 的最佳用法，因为它依赖于 I/O 完成端口，并且在执行冗长的操作期间不会独占服务器上的任何线程。

---

第二种情况更简单(实际上不需要异步 Controller ):

public class BackgroundController : Controller
{
    public ActionResult Export(int id)
    {
        // Fire and forget some lengthy operation
        Task.Factory.StartNew(() => DoLengthyOperation(id));
        // return immediately
        return Json(new { success = true }, JsonRequestBehavior.AllowGet);
    }
}

这是一个 nice article on MSDN在异步 Controller 上。