CODEWITHSUNDEEP
c#.netvisual-studiolinq
Alex Gordon
Alex Gordon

Reputation: 60741

Can selecting an anonymous type be null?

I am going through a codereview and seeing something suspicious.

In the snippet below can result ever be NULL ?

        var result = (from number in _cmContext.SrvLocationWarmLine
                      where String.Compare(number.CurrentWarmLine, startingRange, StringComparison.Ordinal) >= 0
                            && String.Compare(number.CurrentWarmLine, endingRange, StringComparison.Ordinal) <= 0
                      orderby number.CurrentWarmLine descending
                      select new { Number = number.CurrentWarmLine }).FirstOrDefault();

More generally: when applying FirstOrDefault against a select, can the result ever be null?

Upvotes: 1

Views: 867

Answers (1)

Ren&#233; Vogt
Ren&#233; Vogt

Reputation: 43886

Yes. The result is null if the sequence is empty.
This happens if no number in _cmContext.SrvLocationWarmLine matches the condition in the where clause.

In general FirstOrDefault() (without a predicate argument) returns null for an empty sequence (no matter if that sequence was returned by a select or from something different).

The FirstOrDefault<T>(this IEnumerable<T>, Predicate<T>) returns null if there is no element in the sequence matching the predicate.

Note that the select in the query syntax is translated into a Select(...) method call.

Edit: of course the above applies only if the type of the elements of the final sequence is a reference type. For value types the result would be default(type), e.g. 0 for an int.

Upvotes: 3

Related Questions