Is it correct if i am using await + ToListAsync() over IQueryable which is not define as a task

asp.net-mvc-5 async-await asynchronous c# entity-framework-6

Question

I am using asp.net MVC-5 with EF-6, and I am not sure if using await + ToListAsync is valid. For example, I have the following repository method which returns an IQueryable :-

public IQueryable<TSet> getAllScanEmailTo()
{
    return t.TSets.Where(a=>a.Name.StartsWith("ScanEmail"));    
}

And I am calling it as follow:-

var emailsTo = await repository.getAllScanEmailTo().ToListAsync();

In the beginning, I thought I will get an error because I am using "await" a method which is not defined as a task, but the above worked well, so can anyone advice on this, please ?

1
12
3/29/2020 9:11:25 AM

Accepted Answer

At the beginning I thought I will get an error because I am using "await" a method which is not defined as a task, but the above worked well

Actually, you are awaiting a method which returns a Task<T>, where T is a List<TSet>. If you look at the extension method QueryableExtensions.ToListAsync, you'll see that it returns a Task<List<TSource>>. You are asynchronously waiting on this method to query the database, create the list and return it back to the caller. When you await on such a method, the method wont return until the operation has completed. async-await makes your code feel synchronous, while execution is actually asynchronous.

21
3/29/2020 9:12:06 AM

Popular Answer

Actually there is no problem because you are awating the ToListAsync() not the getAllScanEmailTo().

EDIT: To see how async-await pattern is working you can see this link. Here is a usefull image from there

enter image description here



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