LINQ select new Async/Await

Question

I currently have a asynchronous query as follows which is fine and allows me to use the FirstOrDefaultAsync / ToListAsync methods.

 public async Task<X> FindXAsync(int x)
 {
      var q = from c in context.X
              where c.Id == x
              select c;

      return await q.FirstOrDefaultAsync();
 }

However I am attempting to extend that query to select into a new class

public async Task<XClass> FindXAsync(int x)
{
     var q = from c in context.X
            where c.Id == x
            select new XClass (
            c.Id,c.Header .........
            );

     return await q.FirstOrDefaultAsync();
}

For the above you can no longer use the FirstOrDefaultAsync() only FirstOrDefault(), I was wondering what would be the most efficient way to get this functionality into an asynchronous method. Thanks, Chris

Answer 1

In this case, the easiest answer is probably just to do the (asynchronous) first selection, and then create the type you need:

public async Task<XClass> FindXAsync(int x)
{
  var q = from c in context.X
          where c.Id == x
          select c;
  var c = await q.FirstOrDefaultAsync();
  return new XClass (
           c.Id,c.Header .........
  );
}

Answer 2

尝试使用通用类型化参数：

return await q.FirstOrDefaultAsync<XClass>();