在 c# 的 foreach 循环中调用 API

Question

I have the following function that call my API

private async void applyMe(int id, string data)
{
   string url = $"https://localhost:44382/api/isc/getdata?id=" + id + "&data=" + data;
   ApiHelper.InitializeClient();
   string _apiResult = await APIProcessor.LoadApi(url);     
}

API Helper

public static class ApiHelper
{
    public static HttpClient ApiClient { get; set; }
    public static void InitializeClient() 
    {
        ApiClient = new HttpClient();
        ApiClient.DefaultRequestHeaders.Accept.Clear();
        ApiClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/jason"));
    }
}

APIProcessor

public class APIProcessor
{
    public static async Task<string> LoadApi(string url)
    {
        using (HttpResponseMessage response = await ApiHelper.ApiClient.GetAsync(url))
        {
            if (response.IsSuccessStatusCode)
            {
                string _apiResult = await response.Content.ReadAsStringAsync();
                return _apiResult;
            }
            else
            {
                throw new Exception(response.ReasonPhrase);
            }
        }
    }
}

I want to call my API inside foreach loop as below

using (myEntities _context = new myEntities ())
{
    foreach (var item in _context.items.Where(s => s.id >= 1 && s.id <= 500))
      {
          applyMe(item.id, item.data);
      }
 }

The API not calling yet because of async await :( Please how can I solve this issue?

Thanks in advance

Answer 1

Use Task.WhenAll(). It returns an awaitable that will get completed when all other tasks are finished. In the end you need to wait without blocking the thread. see microsoft doc

using (myEntities _context = new myEntities ())
{
    await Task.WhenAll(_context.items
                               .Where(s => s.id >= 1 && s.id <= 500)
                               .Select(s => applyMe(item.id, item.data))
                      );
}

Important! The applyMe should return a Task and not remain void. The async void pattern is not recommended.

Answer 2

You could use IAsyncEnumerable<MyModel> ( docs )

public IAsyncEnumerable<MyModel> GetItems()
{
    IQueryable<T> query = this._context.items;

    query = query.Where(s => s.id >= 1 && s.id <= 500);

    return query.AsAsyncEnumerable();
}

And use it with:

IAsyncEnumerable<MyModel>> items = GetItems();
await foreach (var myModel in items)
{
    //Call external api         
}                

Answer 3

Two small adjustments to make this work: First Task iso void

private async Task getData(int id, string data)
{
    string url = $"https://localhost:44382/api/isc/getdata?id=" + id + "&data=" + data;
    ApiHelper.InitializeClient();
    string _apiResult = await APIProcessor.LoadApi(url);     
}

and second, await the getData call

using (myEntities _context = new myEntities ())
{
    foreach (var item in _context.items.Where(s => s.id >= 1 && s.id <= 500))
      {
          await getData(item.id, item.data);
      }
 }