LinQ distinct with custom comparer leaves duplicates

Question

I\'ve got the following classes:

public class SupplierCategory : IEquatable
{
    public string Name { get; set; }
    public string          


        

Answer 1

Your problem is that you didn't implement IEqualityComparer correctly.

When you implement IEqualityComparer, you must implement GetHashCode so that any two equal objects have the same hashcode.

Otherwise, you will get incorrect behavior, as you're seeing here.

You should implement GetHashCode as follows: (courtesy of this answer)

public int GetHashCode(List obj) {
    int hash = 17;

    foreach(var value in obj)
        hash = hash * 23 + obj.GetHashCode();

    return hash;
}

You also need to override GetHashCode in SupplierCategory to be consistent. For example:

public override int GetHashCode() {
    int hash = 17;
    hash = hash * 23 + Name.GetHashCode();
    hash = hash * 23 + Parent.GetHashCode();
    return hash;
}

Finally, although you don't need to, you should probably override Equals in SupplierCategory and make it call the Equals method you implemented for IEquatable.