Perform order by without implementing icomparable because getting issue at least one object must implement icomparable

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I have List of `Person` class as

var list = List<person>();

I want to order the list in descending order based on `PersonId`

var newlist = list.OrderByDescending(x => x.PersonId).ToList();

The class `Person` is created some other team and I don't want change the class by implementing `IComparable`.

Is there any way that I can use order by without implementing `IComparable`.

Any help?

What I have tried:

var newlist = list.OrderByDescending(x => x.PersonId).ToList();

Posted 6-Dec-17 0:30am

Ritesh Koul

Updated 6-Dec-17 2:06am

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F-ES Sitecore 6-Dec-17 6:47am

Your code should work, you don't need Person to implement IComparable.

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OriginalGriff · Answer 1 · 2017-12-06T02:05:00

The problem is not the Person class, it's the type of PersonId: if it's integer, that'll work fine:

class Program
    {
    static void Main(string[] args)
        {
        var list = new List<Person>();
        list.Add(new Person(){PersonId = 3});
        list.Add(new Person(){PersonId = 7});
        list.Add(new Person(){PersonId = 9});
        list.Add(new Person(){PersonId = 42});
        var newlist = list.OrderByDescending(x => x.PersonId).ToList();
        Console.ReadLine();
        }
    }
class Person
    {
    public int PersonId {get; set; }
    }

But if the PersonId isn't IComparable there is no real way to be sure that the ordering is correct, other than arranging a comparator. But you won't get an error even like this:

class Program
    {
    static void Main(string[] args)
        {
        var list = new List<Person>();
        list.Add(new Person(){PersonId = 3});
        list.Add(new Person(){PersonId = 7});
        list.Add(new Person(){PersonId = 9});
        list.Add(new Person(){PersonId = 42});
        var newlist = list.OrderByDescending(x => x.p).ToList();
        Console.ReadLine();
        }
    }
class Person
    {
    public int PersonId {get; set; }
    public Person p { get; set; }
    }
}

You'll just get the same order you started with, probably.