Check if single() LINQ return NULL

Question

I have a LINQ query that should return either a single result or not results. I call Single() to get the result like this:

var propertyDataSource = (from x in myCollection
                          where SomeCondition(x)
                          select x).Single();

This works okay when my query has a single result, but if there are no results it throws a System.InvalidOperationException with the message Sequence contains no elements.

How can I fix this?

Answer 1

Use SingleOrDefault instead.

Single throws an exception when the enumeration does not contain exactly one element, SingleOrDefault<T> returns default(T) (which is null for reference types) when called on empty enumerations instead. Note that both will throw if there is more than one element in the enumeration.

Answer 2

By design, Single will throw an exception when the sequence is empty. Use SingleOrDefault to return null when your sequence is empty.

Answer 3

.SingleOrDefault() will return the single matching object or the default value (which is null for reference types). You will have to handle the null case yourself though because you'll end up with a NullReferenceException pretty quickly.

As a side note, you should use .Any() instead of .Count() > 0 to avoid iterating over your entire dataset when using IEnumerables.

Answer 4

.FirstOrDefault() returns null (or default of the type) if nothing exists (no match is found), .Single() will expect exactly one match. .SingleOrDefault() will return null (or default of the type) if nothing exists but will throw exception if you have more than one match.