MVC5: Asynchronous child actions Not supported

[sanilpaul]

what is the recommended way to execute asynchronous actions (database access) through child actions in MVC5? I understand its very subjective to what i do in the child action. In my case, its only async queries to sql server using EF6.

Is wrapping in a task.run has any side effects in this case or is there any better way microsoft recommends other than changing to Synchronous?

@Html.Action("SampleChildAction)

public PartialViewResult SampleChildAction()
{
    Task.Run(async () => { await asyncMethod(); }).Result; 
    return PartialView("_SampleChildActionView");
}

I couldn't locate anything guidance from microsoft. I would appreciate any help.
https://justsimplycode.com/2016/09/04/child-action-in-mvc-5-does-not-support-async/
dotnet/aspnetcore#343

[Eilon]

Unfortunately I'm not aware of any good/clean way to do this. It's a limitation of how Child Actions are implemented in MVC, which I don't think there's a good way to work around.

[alohaninja]

PartialViewResult is single-threaded so you can't benefit from async - in fact it blocks the app from executing entirely. Here are some options we use to work around it - keep in mind it still executes your child actions synchronously...

Using SynchronizationContext

private T InvokeAsyncMethod<T>(Func<Task<T>> func)
{
    var syncContext = SynchronizationContext.Current;
    SynchronizationContext.SetSynchronizationContext(null);

    var result = func.GetResult();

    SynchronizationContext.SetSynchronizationContext(syncContext);

    return result;
}

Using Task Library

private T InvokeAsyncMethod<T>(Func<Task<T>> func)
{
    return Task.Factory.StartNew(func)
        .Unwrap()
        .GetAwaiter()
        .GetResult();
}

To use this approach - just call your async method inline...

var user = InvokeAsyncMethod(() => user.getAsync(userId));

PartialViews have been superseded by ViewComponents in ASP.NET Core .

[benmccallum]

Dude, best timing for an answer here. Had this issue just yesterday. Thanks @alohaninja !

[benmccallum]

I think there's a typo in the first approach. Should it be var result = func().GetAwaiter().GetResult()?

[alohaninja]

I think there's a typo in the first approach. Should it be var result = func().GetAwaiter().GetResult()?

Corrected - nice catch! 🎉