using System;

using System.Text;

using System.IO;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    class BuyDTO

    {

        public int SessionId { get; set; }

        public int ArticleId { get; set; }

        public override bool Equals(object obj)

        {

            return obj is BuyDTO dto && SessionId == dto.SessionId && ArticleId == dto.ArticleId;

        }

        public override int GetHashCode()

        {

            int hashCode = 2118541809;

            hashCode = hashCode * -1521134295 + SessionId.GetHashCode();

            hashCode = hashCode * -1521134295 + ArticleId.GetHashCode();

            return hashCode;

        }

    }

    public static void Main()

    {

        var samples = new List<BuyDTO>

        {

            new BuyDTO { SessionId = 0, ArticleId = 0 },

            new BuyDTO { SessionId = 1, ArticleId = 1 },

            new BuyDTO { SessionId = 2, ArticleId = 2 },

            new BuyDTO { SessionId = 3, ArticleId = 3 },

            new BuyDTO { SessionId = 3, ArticleId = 3 }

        };

        var result = samples

            .Select(e => new BuyDTO

                    {

                        SessionId = e.SessionId,

                        ArticleId = e.ArticleId

                    });

        Console.WriteLine("first pass");

        foreach(var e in result)

            Console.WriteLine("dto (articleId: {0}, sessionId: {1})", e.ArticleId, e.SessionId);

        Console.WriteLine("second pass");

        result = result.Distinct();;

        foreach(var e in result)

            Console.WriteLine("dto (articleId: {0}, sessionId: {1})", e.ArticleId, e.SessionId);

    }

}