In Linq, what's the difference between .FirstOrDefault and .SingleOrDefault

Question

I don't know the difference between FirstOrDefault and SingleOrDefault. When should I use the first and when should I use the second?

Answer 1

FirstOrDefault() is for when zero or more results are expected to be present in the input collection and the call returns the first item if there are multiple results, Default if none.

SingleOrDefault() is for when zero or one result is expected in the input collection and the call returns the one result if exactly one result is present, Default if no results and exception if more than one result.

Answer 2

SingleOrDefault will throw a "Sequence contains more than one element" exception if more than one item exists.