空条件运算符和LINQ

Question

There is my code (it is used in net core project):

 var list = await user.RelatedEntityCanBeNull?.ToListAsync();

It throws NullReferenceException if RelatedEntityCanBeNull is null for user. Why doesn't the expression return null?

Answer 1

The await operator expects an awaitable Task object. The Null conditional operator returns null and await null results in a NullReferenceException .

You have to change your code to

List list = null;
if (user?.RelatedEntityCanBeNull != null)
   list = await user.RelatedEntityCanBeNull.ToListAsync();

or

var list = user?.RelatedEntityCanBeNull == null ? null : await user.RelatedEntityCanBeNull.ToListAsync();