Question

I have a list of Foo's.

Foo has a CreateDate of type DateTime?

I want to get the oldest Foo. I tryed with the intuitive way, but I get a possible System.InvalidOperationException.

DateTime oldestFoo = 
(from f in allFoos where f.CreateDate.HasValue select f.CreateDate.Value).Min(); 

Is there something I missed or is it just not possible this way?

I can do it without LinQ this way, but I want to learn the other approach too.

DateTime oldestFoo = DateTime.MaxValue;
foreach (var foo in allFoos)
{
    if (foo.CreateDate.HasValue && oldestFoo > foo.CreateDate)
    {
        oldestFoo = (DateTime)foo.CreateDate;
    }
}

Answer 1

Just in case you’re still stuck, you might want to consider using DefaultIfEmpty – see if this helps:

DateTime oldestFoo = allFoos.Where(f => f.CreateDate.HasValue)
                            .Select(f => f.CreateDate.Value)
                            .DefaultIfEmpty(DateTime.MaxValue)
                            .Min();

I don’t think you want to use GetValueOrDefault within your query, as otherwise you’ll still have a problem if the first query returns no results at all.