using System;

using System.Collections.Generic;

using System.Text;

using System.Threading;

using System.Linq;



namespace Leaf

{

    public class Test5

    {

        public static void Main(string[] args)

        {

            List<DbInfo> list = new List<DbInfo>()

            {

                new DbInfo(){ DbId=1,HostId=1 },    

                new DbInfo(){ DbId=2,HostId=1 },

                new DbInfo(){ DbId=3,HostId=2 },

                new DbInfo(){ DbId=4,HostId=2 }

            };



            //todo: 如何将list中的对象，group by HostId, 每个HostId保留一条记录? (不要用循环)

            //如上面的list, 最终结果会保留 DbId = 1 和 3

           



            Console.ReadLine();

        }

    }



    public class DbInfo

    {

        public long DbId { get; set; }

        public long HostId { get; set; }

    }

}

var selected = list.GroupBy(v => v.HostId).Select(it => it.First()).ToList();

            //selected.ForEach(v => Console.WriteLine(v.DbId));

var selected1 = from dbinfo in list

                            group dbinfo by dbinfo.HostId into list2

                            select new

                       &n