跳过然后在可空的对象上

Question

I have a query which should be ordered like that:

var list = new List<MonthClosureViewModel>();
var orderedList = list
    .OrderByDescending(x => x.Project)
    .ThenByDescending(x => x.ChargeLine)
    .ThenByDescending(x => x.DomesticSite) //<- x.DomesticSite might be null sometimes
    .ThenByDescending(x => x.ChargeSite)   //<- x.ChargeSite   might be null sometimes
    .ThenByDescending(x => x.RateGroup)
    .ThenByDescending(x => x.ApprovedHrs)
    .ThenByDescending(x => x.NotApprovedHrs);

public class MonthClosureViewModel
{
    public Project Project { get; set; }
    public ChargeLine ChargeLine { get; set; }
    public Site DomesticSite { get; set; }
    public Site ChargeSite { get; set; }
    public RateGroup RateGroup { get; set; }
    public decimal Rate { get; set; }
    public decimal ApprovedHrs { get; set; }
    public decimal NotApprovedHrs { get; set; }
}

But if any object is null (totally by design) this query fails. How can I put null values at the end or skip ordering if object is null?

ADDED: as @LasseV.Karlsen mentioned I might have ANOTHER problem. I really got ArgumentNullException , but the reason was not behind some object were null (I saw it in debugger and falsely thought that it was my problem). The real reason was as @RaphaëlAlthaus mentioned that I didn't implement IComparable<> at ANY of my classes in MonthClosureViewModel ...

After I've done it everything start working as intended even if object is null

Answer 1

You'll need to define defaultSite and defaultChargeSite to be either smaller or larger than all the other objects in their class

var list = new List<MonthClosureViewModel>();
var orderedList = list
     .Where(x => x != null);
    .OrderByDescending(x => x.Project)
    .ThenByDescending(x => x.ChargeLine)
    .ThenByDescending(x => x.DomesticSite==null?defaultSite:x.DomesticSite) //<- x.DomesticSite might be null sometimes
    .ThenByDescending(x => x.ChargeSite==null?defaultChargeSite:x.ChargeSite)   //<- x.ChargeSite   might be null sometimes
    .ThenByDescending(x => x.RateGroup)
    .ThenByDescending(x => x.ApprovedHrs)
    .ThenByDescending(x => x.NotApprovedHrs);

Answer 2

You try to order by complex properties, which is (as you mentionned) the real problem.

To make it possible you'll have to, either

1. implement IComparable<T> on your classes

2. use other overloads of OrderBy / OrderByDescending, which take also an IComparer<TKey> as argument ( msdn for the OrderBy overload)

3. Use a simple property of the complex property in your order by clause (with null check. In this case, the null check becomes necessary to avoid a Null Reference Exception) :

For example :

.OrderByDescending(x => x.Project == null ? string.Empty : x.Project.Name)