using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

                    List<Group> _groups = new List<Group>();

            List<CategoryRoot> _categoryRoots = new List<CategoryRoot>();

            List<Category> _categories = new List<Category>();

​

            _categories.Add(new Category { Id = 1, Name = "C 1", CategoryRoot_Id = 1 });

            _categories.Add(new Category { Id = 2, Name = "C 2", CategoryRoot_Id = 1 });

            _categories.Add(new Category { Id = 3, Name = "C 3", CategoryRoot_Id = 3 });

​

            _categoryRoots.Add(new CategoryRoot { Id = 1, Name = "CR 1", Group_Id = 1, Categories = _categories.Where(p => p.CategoryRoot_Id == 1).ToList() });

            _categoryRoots.Add(new CategoryRoot { Id = 2, Name = "CR 2", Group_Id = 1, Categories = _categories.Where(p => p.CategoryRoot_Id == 2).ToList() });

            _categoryRoots.Add(new CategoryRoot { Id = 3, Name = "CR 3", Group_Id = 2, Categories = _categories.Where(p => p.CategoryRoot_Id == 3).ToList() });

            _categoryRoots.Add(new CategoryRoot { Id = 4, Name = "CR 4", Group_Id = 3, Categories = _categories.Where(p => p.CategoryRoot_Id == 4).ToList() });

​

            _groups.Add(new Group { Id = 1, Name = "Group A", CategoryRoots = _categoryRoots.Where(p => p.Group_Id == 1).ToList() });

            _groups.Add(new Group { Id = 2, Name = "Group B", CategoryRoots = _categoryRoots.Where(p => p.Group_Id == 2).ToList() });

            _groups.Add(new Group { Id = 3, Name = "Group C", CategoryRoots = _categoryRoots.Where(p => p.Group_Id == 3).ToList() });

            _groups.Add(new Group { Id = 4, Name = "Group D", CategoryRoots = _categoryRoots.Where(p => p.Group_Id == 4).ToList() });

​

​

            var results = (from g in _groups

                         join cr in _categoryRoots on g.Id equals cr.Group_Id into gcr

                         from lgc in gcr.DefaultIfEmpty(new CategoryRoot())

                         join c in _categories on lgc.Id equals c.CategoryRoot_Id into ccr

                         from lccr in ccr.DefaultIfEmpty()

                         select new GroupCategory

                         {

                             Id = g.Id,

                             Name = g.Name,

                             CategoryRoot_Id = lgc == null ? 0: lgc.Id,

                             CategoryRootName = lgc == null ? "": lgc.Name,

                             Category_Id = lccr == null ? 0: lccr.Id,

                             CategoryName = lccr == null ? "": lccr.Name

                         }).ToList();

            foreach (var result in results)

            {

                //Console.WriteLine("Id:{0} Name:{1} CategoryRoot_Id:{2} CateoryName:{3} Category_Id:{4} CategoryName:{5}", result.Id, result.Name, result.CategoryRoot_Id, result.CategoryRootName, result.Category_Id, result.CategoryName);

​

                Console.WriteLine("Id:{0} Name:{1} CR:{2} CRN:{3} C:{4} CName:{5}", result.Id, result.Name, result.CategoryRoot_Id, result.CategoryRootName, result.Category_Id, result.CategoryName);

            }

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

    }

    public class GroupCategory

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public int CategoryRoot_Id { get; set; }

        public string CategoryRootName { get; set; }

        public int Category_Id { get; set; }

        public string CategoryName { get; set; }

​

    }

​

    public class Group

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public IEnumerable<CategoryRoot> CategoryRoots { get; set; }

    }

    public class CategoryRoot

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public int Group_Id { get; set; }

        public Group Group { get; set; }

        public IEnumerable<Category> Categories { get; set; }

​

    }

    public class Category

    {

        public int Id { get; set; }

        public string Name { get; set; }

        public int CategoryRoot_Id { get; set; }

        public CategoryRoot CategoryRoot { get; set; }

    }

}