任务不包含如果在一行代码中完成的位置的定义

Question

Why does this work if I split the code into two lines:

List<Foo> foos = await _repo.GetFoos();
foos = foos.Where(x => x.FooType != FooType.A).ToList();

But doesn't work when I combine them and do the Where on the same line?

List<Foo> foos = await _repo.GetFoos().Where(x => x.FooType != FooType.A).ToList();

This produces an error:

Task<List<Foo>> does not contain a definition for 'Where`...

Answer 1

You should use await like this:

List<Foo> foos = (await _repo.GetFoos()).Where(x => x.FooType != FooType.A).ToList();

That's because .Where() in await _repo.GetFoos().Where() is applied to _repo.GetFoos() not result of await _repo.GetFoos() .

Answer 2

The await is applied to the object returned by the entire expression.

You are attempting to use Enumerable.Where on the Task returned by _repo.GetFoos which is invalid.

You could enclose the await _repo.GetFoos() in parentheses to force that to be evaluated first, then Enumerable.Where would be performed on the resultant IEnumerable .