如何将输出值绑定到异步Azure函数？

Question

如何将输出绑定到异步函数？将参数设置为out的常用方法不适用于异步函数。

实施例

using System;

public static async void Run(string input, TraceWriter log, out string blobOutput)
{
    log.Info($"C# manually triggered function called with input: {input}");
    await Task.Delay(1);

    blobOutput = input;
}

这会导致编译错误：

[timestamp] (3,72): error CS1988: Async methods cannot have ref or out parameters

使用绑定（fyi）

{
  "bindings": [
    {
      "type": "blob",
      "name": "blobOutput",
      "path": "testoutput/{rand-guid}.txt",
      "connection": "AzureWebJobsDashboard",
      "direction": "out"
    },
    {
      "type": "manualTrigger",
      "name": "input",
      "direction": "in"
    }
  ],
  "disabled": false
}

Answer 1

有几种方法可以做到这一点：

将输出绑定到函数的返回值（最简单）

然后您只需返回函数中的值即可。您必须将输出绑定的名称设置为$return才能使用此方法

代码

public static async Task<string> Run(string input, TraceWriter log)
{
    log.Info($"C# manually triggered function called with input: {input}");
    await Task.Delay(1);

    return input;
}

装订

{
  "bindings": [
    {
      "type": "blob",
      "name": "$return",
      "path": "testoutput/{rand-guid}.txt",
      "connection": "AzureWebJobsDashboard",
      "direction": "out"
    },
    {
      "type": "manualTrigger",
      "name": "input",
      "direction": "in"
    }
  ],
  "disabled": false
}

将输出绑定到IAsyncCollector

将输出绑定到IAsyncCollector并将您的项目添加到收集器。

当您有多个输出绑定时，您将要使用此方法。

代码

public static async Task Run(string input, IAsyncCollector<string> collection, TraceWriter log)
{
    log.Info($"C# manually triggered function called with input: {input}");
    await collection.AddAsync(input);
}

装订

{
  "bindings": [
    {
      "type": "blob",
      "name": "collection",
      "path": "testoutput/{rand-guid}.txt",
      "connection": "AzureWebJobsDashboard",
      "direction": "out"
    },
    {
      "type": "manualTrigger",
      "name": "input",
      "direction": "in"
    }
  ],
  "disabled": false
}

Answer 2

我还没有声誉可以发表评论，但在上面的Zain Rizvi的代码中，应该说IAsyncCollector：

public static async Task Run(string input, IAsyncCollector<string> collection, 
TraceWriter log)
{
    log.Info($"C# manually triggered function called with input: {input}");
    await collection.AddAsync(input);
}

Answer 3

异步方法可以正常返回值，但是你不应该返回纯类型的值，而是使用Task，如下所示：

 public static async Task<string> Run(string input, TraceWriter log, string blobOutput)
    {
        log.Info($"C# manually triggered function called with input: {input}");
        await Task.Delay(1);

        blobOutput = input;
        return blobOutput;
    }