Getting "The connection does not support MultipleActiveResultSets" in a ForEach with async-await

You need to add attribute MultipleActiveResultSets in connection string and set it to true to allow multiple active result sets.

 "Data Source=MSSQL1;" & _  
    "Initial Catalog=AdventureWorks;Integrated Security=SSPI;" & _  
    "MultipleActiveResultSets=True"  

Read more at: https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/sql/enabling-multiple-active-result-sets

That code starts a Task for each item in the list, but does not wait for the each task to complete before starting the next one. Inside each Task it waits for the update to complete. Try

 Enumerable.Range(1, 10).ToList().ForEach(async i => await Task.Delay(1000).ContinueWith(t => Console.WriteLine(DateTime.Now)));

Which is equivalent to

    foreach (var i in Enumerable.Range(1, 10).ToList() )
    {
        var task = Task.Delay(1000).ContinueWith(t => Console.WriteLine(DateTime.Now));
    }

If you're in a non-async method you will have to Wait(), not await each task. EG

    foreach (var i in Enumerable.Range(1, 10).ToList() )
    {
        var task = Task.Delay(1000).ContinueWith(t => Console.WriteLine(DateTime.Now));
        //possibly do other stuff on this thread
        task.Wait(); //wait for this task to complete
    }

The problem is the ForEach method is not an asynchronous method. It will not await the Task returned by your lambda. Running that code will fire every task and not wait for completion of any of them.

General point: marking a lambda as async does not make a synchronous method you pass it into behave asynchronously.

Solution: you will need to use a foreach loop which awaits the tasks' completion.

eg: foreach (var x in xs) await f(x);

You can wrap that in a helper method if you prefer.

(I know it's an old question, but I don't think it was clearly answered)