using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

    var firstList = new List<SomeObject> {

        new SomeObject { Id = 1, Name = "Rose" } ,

        new SomeObject { Id = 2, Name = "Mary" } ,

        new SomeObject { Id = 3, Name = "Gozzi" }

    };

    var secondList = new List<SomeObject> {

        new SomeObject { Id = 1, Name = "Rose" } ,

        new SomeObject { Id = 2, Name = "Mary" } ,

        new SomeObject { Id = 3, Name = null } ,

    };

​

    //Get elements in first list which already exist in second list. Use Id and Name as filters.

    var alreadyExistingItemsInSecondList = firstList.SelectMany(p => secondList.Where(q => q.Id == p.Id && q.Name == p.Name));

    foreach(var v in alreadyExistingItemsInSecondList)

    {

        Console.WriteLine(String.Format("First list item with Id:{0} and Name:{1}",v.Id,v.Name));

    }

​

    //Console.WriteLine(result); 

    }

}

​

public class SomeObject

{

​

    public int Id { get; set; }

    public string Name { get; set; }

​

}