如何在另一个列表中过滤对象列表

Question

I need some help to filter a list of objects inside another list of objects.

Currently I am able to filter the FirstLevel object to return only the SecondLevel objects that matches the criteria (having the Id within the list), and if it happens to have a ThirdLevel filter, I need to return only the SecondLevel containing the ThirdLevel object that matches the criteria.

What I need is for the ThirdLevel array to contain only the ones that matches the criteria.

Am I able to do that within a single Linq query?

EDIT: Humanly understandable(??) example: Let's say I have a closet, and in this closet I have lots of drawers. Now in these drawers I have several pairs of socks, each with a diferent color. What I need is to be able to filter the drawers to show me only those that contain black socks while removing the other colors from the drawer. (dunno if that made sense)

Below is an example code:

using System;
using System.Text;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace MyNamespace
{
    public class Program
    {
        public static void Main(string[] args)
        {
            List<int> filterSecondLevel = new List<int>(){1, 2};
            List<int> filterThirdLevel = new List<int>(){3};

            ThirdLevel _3a = new ThirdLevel(){Id=1};
            ThirdLevel _3b = new ThirdLevel(){Id=2};
            ThirdLevel _3c = new ThirdLevel(){Id=3};
            ThirdLevel _3d = new ThirdLevel(){Id=4};

            List<ThirdLevel> _3la = new List<ThirdLevel>(){_3a,_3b};
            List<ThirdLevel> _3lb = new List<ThirdLevel>(){_3c,_3d};

            SecondLevel _2a = new SecondLevel(){ Id=1, ThirdLevelList=_3la};
            SecondLevel _2b = new SecondLevel(){ Id=2, ThirdLevelList=_3lb};

            List<SecondLevel> _2la = new List<SecondLevel>(){_2a,_2b};

            FirstLevel _1a = new FirstLevel(){ Id=1, SecondLevelList=_2la};

            var result = _1a.SecondLevelList.Where(x => 
                                                          (filterSecondLevel.Count == 0 || filterSecondLevel.Contains(x.Id)) && 
                                                              x.ThirdLevelList.Where(y => 
                                                                  filterThirdLevel.Count == 0 || filterThirdLevel.Contains(y.Id)
                                                      ).ToList().Count > 0
                                                  ).ToList();
        }
    }

    public class FirstLevel
    {
        public int Id {get;set;}
        public List<SecondLevel> SecondLevelList { get; set; }
    }

    public class SecondLevel
    {
        public int Id {get;set;}
        public List<ThirdLevel> ThirdLevelList { get; set; }
    }

    public class ThirdLevel
    {
        public int Id {get;set;}
    }
}

Answer 1

you need to use ANY()

            var result = _1a.SecondLevelList.Where(x =>
                                                          (filterSecondLevel.Count == 0 || filterSecondLevel.Contains(x.Id)) &&
                                                              x.ThirdLevelList.Where(y => filterThirdLevel.Contains(y.Id)).Any())
                                                              .ToList();