异步填充字典 [英] Populate dictionary asynchronously

问题描述

我有一个简单的 foreach 循环(如下所示)，该循环遍历一个集合并进行异步API调用以根据当前的迭代器值获取数据.

I have a simple foreach loop (as below) that iterates over a collection and makes an async API call to fetch data based on the current iterator value.

foreach (var group in groups)
{
    var usersInGroup = await this.tableauService.GetUsersInTableauGroup(group.Id);

    // do work with `usersInGroup`
}

我不想为每个迭代创建一个API调用，而是要为每个API调用创建一个异步任务，并同时执行所有任务，其结果将填充由 group.Id 键控的字典..这可能吗?

Instead of making an API call each iteration, I want to create an async task for each API call and execute them all at the same time, with the results populating a dictionary keyed by group.Id. Is this possible?

在我的脑海中，代码看起来像这样:

In my head, the code would look something like:

IList<Task<string[]>> tasks = new List<Task<string[]>>();
IDictionary<string, string[]> dictionary = new Dictionary<string, string[]>();

foreach (var group in groups)
{
    tasks.Add(this.tableauService.GetUsersInTableauGroup(group.Id));
    // Somehow define callback of each task to hydrate dictionary
}

await Task.WhenAll(tasks);

推荐答案

Task.WhenAll()返回任务的所有值，因此您可以执行以下操作:

Task.WhenAll() returns all the values of the tasks, so you can do something like this:

var tasks = groups
  .Select(async g => new 
  {
    g.Id, 
    Values = await this.tableauService.GetUsersInTableauGroup(g.Id)
  });
var results = await Task.WhenAll(tasks);
var dictionary = results
  .ToDictionary(r => r.Id, r => r.Values);

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