在 lambda 上执行 distinct() 时替换 IEquatable 接口

Question

I have this class which implements the IEquatable<T> interface

public class ArticleDescriptionDetails : IEquatable<ArticleDescriptionDetails>
{
    public string Code { get; set; }
    public string Value { get; set; }
    public bool Hidden { get; set; }

    public bool Equals(ArticleDescriptionDetails other)
    {
        if (ReferenceEquals(null, other)) return false;
        if (ReferenceEquals(this, other)) return true;
        return Code == other.Code;
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        return obj.GetType() == GetType() && Equals((ArticleDescriptionDetails) obj);
    }

    public override int GetHashCode() => ((Code != null ? Code.GetHashCode() : 0) * 397) ^ Hidden.GetHashCode();

    public static bool operator ==(ArticleDescriptionDetails left, ArticleDescriptionDetails right) => Equals(left, right);

    public static bool operator !=(ArticleDescriptionDetails left, ArticleDescriptionDetails right) => !Equals(left, right);
}

I need this beacuse I'm tring to return an IEquatable<ArticleDescriptionDetails> in this way:

return result.OrderBy(x => x.Code).ThenBy(y => y.Hidden).Distinct();

Is there a way to do the same thing without using the IEquatable<T> interface?

Answer 1

You could use a DistinctBy method and do

return result.OrderBy(x => x.Code).ThenBy(y => y.Hidden).DistinctBy(z => z.Code); 

But the DistinctBy method doesn't exist in linq but you can find it in the morelinq package https://www.nuget.org/packages/MoreLinq.Source.MoreEnumerable.DistinctBy/

But it's also easy to code your own version of the method : You first need to define an IEqualityComparer

    public class KeyEqualityComparer<T, K> : IEqualityComparer<T>
    {
        private readonly Func<T, K> selector;

        public KeyEqualityComparer(Func<T, K> keySelector)
        {
            selector = keySelector;
        }

        public bool Equals(T x, T y)
        {
            return selector(x).Equals(selector(y));
        }

        public int GetHashCode(T obj)
        {
            return selector(obj).GetHashCode();
        }
    }

And the you can use this IEqualityComparer in the Distinct method :

        public static IEnumerable<T> DistinctBy<T, K>(this IEnumerable<T> list, Func<T, K> keySelector)
        {
            var equalityComparer = new KeyEqualityComparer<T, K>(keySelector);
            return list.Distinct(equalityComparer);
        }