c# async when returning LINQ

问题

I've just realised that this code:

    public async Task<List<Review>> GetTitleReviews(int titleID)
    {
        using (var context = new exampleEntities())
        {
            return await context.Reviews.Where(x => x.Title_Id == titleID).ToList();        
        }
    }

...will not work as async methods cannot await LINQ expressions. I've did some searches but only managed to find some overcomplicated solutions.

How should functions which return LINQ expressions be converted to async versions?

回答1:

Add the System.Data.Entity namespace and take advantage of the Async extension methods

In this case ToListAsync should do the trick

using System.Data.Entity;

public async Task<List<Review>> GetTitleReviews(int titleID)
{
    using (var context = new exampleEntities())
    {
        return await context.Reviews.Where(x => x.Title_Id == titleID).ToListAsync();        
    }
}

回答2:

Technically, that method doesn't return a lambda. It returns a List<Review>.

It's true what you posted won't compile. But this would:

public async Task<List<Review>> GetTitleReviews(int titleID)
{
    using (var context = new exampleEntities())
    {
        return await Task.Run(() => context.Reviews.Where(x => x.Title_Id == titleID).ToList());
    }
}

If that doesn't answer your question, maybe you can be more clear about exactly what you're trying to accomplish and why the above doesn't do it.

来源：https://stackoverflow.com/questions/26643752/c-sharp-async-when-returning-linq