LINQ Distinct()

using System;
using System.Collections.Generic;
using System.Linq;

namespace LinqTest
{
    class Program
    {

        static void Main()
        {
            List<Product> listProduct = new List<Product> {
                    new Product{StockNum=,ProductNo="",Tag="a"},
                    new Product{StockNum=,ProductNo="",Tag="a"},
                    new Product{StockNum=,ProductNo="",Tag="a"},
                    new Product{StockNum=,ProductNo="",Tag="b"},
                    new Product{StockNum=,ProductNo="",Tag="b"},
                    new Product{StockNum=,ProductNo="",Tag="b"},
                    new Product{StockNum=,ProductNo="",Tag="c"},
                    new Product{StockNum=,ProductNo="",Tag="d"},
                    new Product{StockNum=,ProductNo="",Tag="e"},
                };

            //去重复
            var listProduct1 = listProduct.Select(s => new
            Product
            {
                StockNum = s.StockNum,
                ProductNo = s.ProductNo,
                Tag = s.Tag
            }).Distinct(new ProductNoComparer()).ToList();

            //输出验证
            listProduct1.ForEach(c =>
            {
                Console.WriteLine("ProductNo={0},StockNum={1},Tag={2}", c.ProductNo, c.StockNum, c.Tag);
            });

            Console.WriteLine("-------------------");

            //去重复
            var listProduct2 = listProduct.Select(s => new
            {
                s.ProductNo,
                s.StockNum,
                s.Tag
            }).Distinct().ToList();

            //输出验证
            listProduct2.ForEach(c =>
            {
                Console.WriteLine("ProductNo={0},StockNum={1},Tag={2}", c.ProductNo, c.StockNum, c.Tag);
            });
            Console.Read();
        }

    }

    /// <summary>
    /// 产品实体类
    /// </summary>
    class Product
    {
        /// <summary>
        /// 库存
        /// </summary>
        public int StockNum { set; get; }

        /// <summary>
        /// 产品编号
        /// </summary>
        public String ProductNo { set; get; }

        /// <summary>
        /// 附属标签
        /// </summary>
        public String Tag { set; get; }
    }

    /// <summary>
    /// 去"重复"时候的比较器(只要ProductNo相同，即认为是相同记录)
    /// </summary>
    class ProductNoComparer : IEqualityComparer<Product>
    {
        public bool Equals(Product p1, Product p2)
        {
            if (p1 == null)
                return p2 == null;
            return p1.ProductNo == p2.ProductNo && p1.StockNum == p2.StockNum && p1.Tag == p2.Tag;
        }

        public int GetHashCode(Product p)
        {
            if (p == null)
                return ;
            return p.ProductNo.GetHashCode();
        }
    }
}