C# 6 null conditional operator check for .Any()?

Question

In the example shown here (and on numerous other websites) with regards to the null-conditional operator, it states that

int? first = customers?[0].Orders.Count(); 

can be used to get the count for the first customer. But this statement does not check for the existence of customers in the collection and can throw an index out of range exception. What should be the correct (preferably single-lined) statement that takes care of checking for the existence of elements?

Answer 1

The null conditional operator is intended for conditionally accessing null but this isn't the issue you're having.

You are trying to access an empty array. You can turn that into a case of accessing null with FirstOrDefault and use the operator on that:

int? first = customers.FirstOrDefault()?.Orders.Count(); 

If the array isn't empty it will operate on the first item, and if it is empty FirstOrDefault will return null which will be handled by the null conditional operator.

Edit: As w.b mentioned in the comments, if you're looking for another item than the first one you can use ElementAtOrDefault instead of FirstOrDefault

Answer 2

You can use LINQ's DefaultIfEmpty, it will yield a singleton IEnumerable in case the collection queried is empty:

int? first = customers?.DefaultIfEmpty().First().Orders.Count();

or if you want to use indexing:

int? first = customers?.DefaultIfEmpty().ToArray()[0].Orders.Count();