Problem using List Except

[thomus07]

 interface IValidationData : IEquatable<IValidationData>
        {
       
        }       

        class Customer : IValidationData
        {
            public string Name { get; set; }
            public int Age { get; set; }            

            public bool Equals(IValidationData otherValue)
            {
                Customer other = otherValue as Customer;

                if (!Name.Equals(other.Name))
                    return false;
                if (!Age.Equals(other.Age))
                    return false;

                return true;
            }

            public override int GetHashCode()
            {
                return Name.GetHashCode() ^ Age.GetHashCode();
            }
        }

    List<Customer> list1 = new List<Customer>();
    List<Customer> list2 = new List<Customer>(); 
    List<Customer> list3 = list2.Except(list1).ToList(); 
// This line is not working why?

I can't use Except method of List, why?

[BioPhysEngr]

Without knowing the exact exception, it's hard to tell. Do you have using System.Linq; at the top of your source file? If not, add it.

The following code compiles for me okay:

List<int> list1 = new List<int>();
list1.Add(2);
list1.Add(3);

List<int> list2 = new List<int>();
list2.Add(2);

List<int> list3 = list1.Except(list2).ToList();

foreach(int i in list3)
    Console.WriteLine(i);

//Prints 3

You can also try defining list3 like:

IEnumerable<int> diff = list1.Except(list2)
List<int> list3 = new List<int>(diff);

However, I'm not sure there is any advantage to doing that.

If neither of those solves your problem, post the exception message and that might help figure out what is wrong.

[thomus07]

I'm not getting any exception, it complies. But it's not getting the required values for list1.Except(list2).

In your example you are using int, so it will work. If you could try with my class pattern, it won't

[foamy]

I did some debugging on your code. It seems if the objects in list1 are the same instances as the ones in list2, the code works. However, if the objects are different instances with the same values, it does not.

this works:

            List<Customer> list1 = new List<Customer>();
            Customer c = new Customer();
            c.Age = 18;
            c.Name = "Kitten";
            list1.Add(c);
            List<Customer> list2 = new List<Customer>();
            //c = new Customer();
            //c.Age = 18;
            //c.Name = "Kitten";
            list2.Add(c);
            c = new Customer();
            c.Age = 28;
            c.Name = "Mitten";
            list2.Add(c);
            List<Customer> list3 = list2.Except(list1).ToList();

this does not:

            List<Customer> list1 = new List<Customer>();
            Customer c = new Customer();
            c.Age = 18;
            c.Name = "Kitten";
            list1.Add(c);
            List<Customer> list2 = new List<Customer>();
            c = new Customer();
            c.Age = 18;
            c.Name = "Kitten";
            list2.Add(c);
            c = new Customer();
            c.Age = 28;
            c.Name = "Mitten";
            list2.Add(c);
            List<Customer> list3 = list2.Except(list1).ToList();

This happens despite the fact that the hashcodes appear to be identical. I'm not able to explain this behavior, but I hope this might help

[Mutant_Fruit]

You more than likely need to override the default equality method too:

public override bool Equals (object other)
{
    return Equals (other as Customer);
}

[thomus07]

Thank you BioPhyEng, Foamy and Mutant fruit for answers.

Mutantfruit, Your solution worked.
Foamy, just found another interesting thing..
If I change the customer class to -
class Customer : IEquatable<Customer>
it's working too...

Looks like except doesn't want Equals method with parameter as an interface