Difference Between Two Lists in EF6 using except doesn't work

Question

I am trying to calculate the Difference between two list my list type has this structure :

public partial class Assistance
{

    public int Id { get; set; }
    public string AssistanceName { get; set; }
    public string AssistanceTell { get; set; }
}

and here is my query :

           List<Assistance> assistanceWithoutExpert;
            AssistanceJurorRepository assistanceJurorRepository = new AssistanceJurorRepository();

            List<Assistance> assistancesWithExpert = assistanceJurorRepository.FindBy(i => i.User.Permission == "Assistance").Select(i => i.Assistance).ToList();
            List<Assistance> AllAssitance = GetAll().ToList();
            assistanceWithoutExpert = AllAssitance.Except(assistancesWithExpert).ToList();
            return assistanceWithoutExpert;

As you can see i have a list that holds all assitances called AllAssitance and a list that hold assitances that has expert called assistancesWithExpert i need to calculate assistanceWithoutExpert.So but after executing the result is all records in AllAssitance why ?

Best regards

Answer 1

You need to use the overload which takes a comparer. It doesn't work out of the box with complex types.

public class AssistanceComparer: IEqualityComparer<Assistance>
{
    public bool Equals(Assistance x, Assistance y)
    {
        return x.ID == y.ID;
    }

    public int GetHashCode(Assistance assistance)
    {
        return assistance.ID.GetHashCode();
    }
}

Usage:

assistanceWithoutExpert = AllAssitance.Except(assistancesWithExpert, new AssistanceComparer()).ToList();