How to Properly Use Async Operations within a ForEach Loop in C#?

Using Async with ForEach

When attempting to utilize async operations within a ForEach loop, one might encounter the issue of receiving an error similar to "The name 'Async' does not exist in the current context." This is because List.ForEach does not readily accommodate async operations.

To resolve this issue, it is recommended to project each element of the list into an asynchronous operation. This can be achieved by using the Select method to create a collection of tasks, each representing an asynchronous operation corresponding to an element in the list.

using (DataContext db = new DataLayer.DataContext())
{
    var tasks = db.Groups.ToList().Select(i => GetAdminsFromGroupAsync(i.Gid));
    var results = await Task.WhenAll(tasks);
}

This approach offers several advantages:

• Proper Error Handling: Exceptions from asynchronous operations cannot be caught with a try/catch block. Using Task.WhenAll ensures that exceptions are propagated, enabling natural exception handling.
• Completion Tracking: By awaiting Task.WhenAll, the code establishes that all asynchronous operations have completed. This knowledge is not readily available when using async void delegates with ForEach.
• Intuitive Syntax: The syntax for retrieving results is more intuitive, as GetAdminsFromGroupAsync implies a return value, allowing for a more natural programming style.

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