using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace JoinTest

{

    public class Program

    {

        public class Faq

        {

            public int Id { get; set; }

            public string Question { get; set; }

        }

​

        public class Like

        {

            public int Id { get; set; }

            public string Type { get; set; }

            public int TypeId { get; set; }

        }

​

        public void Main(string[] args)

        {

            var likesData = new List<Like>

            {

                new Like { Id = 1, Type = "Faq", TypeId = 1 },

                new Like { Id = 2, Type = "Faq", TypeId = 1 },

                new Like { Id = 3, Type = "Faq", TypeId = 1 },

                new Like { Id = 4, Type = "Faq", TypeId = 2 },

                new Like { Id = 5, Type = "User", TypeId = 2 },

            };

​

            var faqsData = new List<Faq>

            {

                new Faq { Id = 1, Question = "Sample Question 1" },

                new Faq { Id = 2, Question = "Sample Question 2" }

            };

​

            var records = (from faq in faqsData

                           join likes in likesData on new { FaqId = faq.Id, Type = "Faq" } equals new { FaqId = likes.TypeId, likes.Type }

                           group faq.Id by likes.TypeId into groupedLikes

                           select new

                           {

                               FaqId = groupedLikes.Key,

                               Likes = groupedLikes.ToList()

                           });

​

            records.ToList().ForEach(x => Console.WriteLine(string.Format("FaqId: {0} has {1} likes", x.FaqId, x.Likes.Count)));

        }

    }

}

​