ASP.NET MVC2是否从jQuery调用AsyncController方法？

Question

我正在尝试学习如何在MVC2中使用AsyncController，但是几乎没有文档/教程。我正在寻找一个普通的控制器方法，有一个非常慢的输出到第三方服务，并将其转换为异步方法。

原始的控制器方法：

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的新控制器：

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调用Export方法：

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

但结果是404 not found (404未找到)错误(未找到背景/导出)。如果我尝试调用Background/Hello或Background/ExportAysnc，则会找到它们。

我做错了什么？

Answer 1

确实有两个用例

1. 你只关心冗长操作的结果
2. 你不关心结果(点火后忘记)

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();
    }
}

现在您可以像这样调用它：

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

现在，因为您已经提到了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);
    }
}

这是异步控制器的最佳用途，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(实际上不需要异步控制器)：

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);
    }
}

这是一个关于异步控制器的nice article on MSDN。