Linq - pulling a value from a null query result - linq-to-sql

Question

I have a linq query that needs to pull a date column out of a row. The expression currently looks like this
myObject.OrderByDescending(s=> s.MyDate).Where(s => s.CRAStatus.Description == "CheckedOut").FirstOrDefault().MyDate)
The problem is that if there are no rows that are "CheckedOut", the query will return a null and attempting to get "MyDate" will throw an exception. We have some verbose solutions, like:
.ForMember(dest => dest.CheckOutDate, opt => opt.MapFrom(src => {
var temp = src.CRAStatusChangeEvents.OrderByDescending(s=> s.MyDate).Where(s => s.CRAStatus.Description == "CheckedOut").FirstOrDefault();
return temp == null ? temp.MyDate : null;
}));
But it would be nice to find something a little more concise. Any Ideas?

Answer 1

Why not
myObject.OrderByDescending(s=> s.MyDate)
.Where(s => s.CRAStatus.Description == "CheckedOut")
.Select(s => s.MyDate as DateTime?)
.FirstOrDefault();
or
myObject.Where(s => s.CRAStatus.Description == "CheckedOut")
.Max(s => s.MyDate as DateTime?);

Answer 2

One option is to set the default if empty to an "empty" instance (think of string.Empty--its a known instance that represents an empty result):
var date = (myObject
.OrderByDescending(s=> s.MyDate)
.Where(s => s.CRAStatus.Description == "CheckedOut")
.DefaultIfEmpty(MyObject.Empty)
.FirstOrDefault()).MyDate;
Here's a snippet that shows how it works:
var strings = new string[]{"one", "two"};
var length =
(strings.Where(s=>s.Length > 5)
.DefaultIfEmpty(string.Empty)
.FirstOrDefault()).Length;
run that and length is 0. Remove the DefaultIfEmpty line and you get a NRE.

Answer 3

var checkedOut = myObject.Where(s => s.CRAStatus.Description == "CheckedOut");
if (checkedOut.Count() > 0) {
var result = checkedOut.Max(s=> s.MyDate).MyDate;
}

Answer 4

How about an extension method?
static class MyObjectEnumerableExtensions
{
public static TMember GetMemberOfFirstOrDefault<TMember>(this IEnumerable<MyObject> items, Func<MyObject, TMember> getMember)
{
MyObject first = items.FirstOrDefault();
if (first != null)
{
return getMember(first);
}
else
{
return default(TMember);
}
}
}
Sample usage:
List<MyObject> objects = new List<MyObject>();
objects.Add(new MyObject { MyDate = DateTime.MinValue });
var filteredObjects = from s in objects where s.MyDate > DateTime.MinValue select s;
DateTime date = filteredObjects.GetMemberOfFirstOrDefault(s => s.MyDate);
Console.WriteLine(date);