Determine sequence contains no element using LINQ [duplicate]

Answer 1

Max() throws an ArgumentNullException if the source doesn't have any elements. You could write an extension method that checks for this and returns a null (or whatever you want) if there aren't any elements.

public static Nullable<DateTime> MaxOrNull(this IEnumerable<DateTime> source)
{
    if (source.Count() == 0)
        return null;
    else
        return source.Max();
}

Answer 2

Try

var d = lst1.Where(q => q <= DateTime.Now).DefaultIfEmpty().Max();

Your result will now contain DateTime.MinValue if there are no matches

Answer 3

I like:

var d = lst1.Where(q => q <= DateTime.Now).OrderByDescending(q => q.DateField).FirstOrDefault();

This will return a null if the list is empty.