using System;

using System.Collections.Generic;

using System.Linq;

​

public class FishTank{

    public int Id;

    public string TankName;

}

​

public class Fish{

    public int Id;

    public int TankId;

    public string Name;

}

​

public class Program

{

    public static void Main()

    {

        List<FishTank> fishTanks = new List<FishTank>();

        fishTanks.Add(new FishTank(){Id = 1, TankName = "Nemo's Palace"});

        fishTanks.Add(new FishTank(){Id = 2, TankName = "Ariel's Layer"});

        List<Fish> fish = new List<Fish>();

        fish.Add(new Fish(){Id = 1, TankId = 1, Name = "Nemo's Mom"});

        fish.Add(new Fish(){Id = 2, TankId = 1, Name = "Nemo's Dad"});

        fish.Add(new Fish(){Id = 3, TankId = 1, Name = "Nemo"});

        fish.Add(new Fish(){Id = 4, TankId = 1, Name = "Nemo's Brother"});

        fish.Add(new Fish(){Id = 5, TankId = 1, Name = "Nemo's Sister"});

        fish.Add(new Fish(){Id = 6, TankId = 2, Name = "Ariel's Mom"});

        fish.Add(new Fish(){Id = 7, TankId = 2, Name = "Ariel's Dad"});

        fish.Add(new Fish(){Id = 8, TankId = 2, Name = "Ariel"});

        fish.Add(new Fish(){Id = 9, TankId = 2, Name = "Ariel's Brother"});

        fish.Add(new Fish(){Id = 10, TankId = 2, Name = "Ariel's Sister"});

        fish.Add(new Fish(){Id = 11, TankId = 2, Name = "Sebastian"});

        var results = 

                fishTanks.GroupJoin(fish, ft => ft.Id, f => f.TankId, ((ft, f) => new {Tank = ft, Fish = f})).ToList();

        foreach(var result in results){

            Console.WriteLine($"Id = {result.Tank.Id}, TankName = {result.Tank.TankName}");

        }

        Console.WriteLine("===================================");

        Console.WriteLine("===================================");

        foreach(var result in results){

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

            Console.WriteLine($"Id = {result.Tank.Id}, TankName = {result.Tank.TankName}");

            foreach(var f in result.Fish){

                Console.WriteLine($"Id = {f.Id}, TankId = {f.TankId}, Name = {f.Name}");

            }

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

        }

    }

}