Ordering a NodaTime Nullable OffsetDateTime

user_1926027 0
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I have a class Appointment that contains a nullable NodaTime.OffsetDateTime property. If I have a list of Appointments, how would I use Linq OrderBy to order this list with the null StartDateTime first then StartDateTime in descending order?

Class Appointment
{
    public OffsetDateTime? StartDateTime { get; set; }
}

I tried doing this

var orderedAppointments = myAppointmentsList
    .OrderByDescending(x => x.StartDateTime is null)
    .ThenByDescending(x => x.StartDateTime, OffsetDateTime.Comparer.Local)
    .ToList();

but I get an error because the OffsetDateTime.Comparer cant handle null values.

I could do something like this

var orderedAppointments = myAppointmentsList
    .OrderByDescending(x => x.StartDateTime ?? StartDateTime.MaxValue, OffsetDateTime.Comparer.Local)
    .ToList();

but StartDateTime doesn't have MaxValue.

What is the recommendation here, create my own OffsetDateTime max value, or is there a better way of doing this that I'm missing?

nodatime nullable sorting c#
1 Answers

So you want the null values first? Then you could use:

var orderedAppointments = myAppointmentsList
    .OrderBy(x => x.StartDateTime.HasValue ? 1 : 0)
    .ThenByDescending(x => x.StartDateTime.GetValueOrDefault(), OffsetDateTime.Comparer.Local)
    .ToList();
user_2842400
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