using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var customers = new List<Customer>()            

        {

            new Customer() {

                Id = Guid.NewGuid().ToString(),

                Name = "Customer1"          

            },

            new Customer() {

                Id = Guid.NewGuid().ToString(),

                Name = "Customer2"          

            }

        };

        var purchases = new List<Purchase>() 

        {

            new Purchase() {                

                Id = Guid.NewGuid().ToString(),

                CustomerId = customers[0].Id,

                Description = "Customer1-Purchase1"         

            },

            new Purchase() {

                Id = Guid.NewGuid().ToString(),

                CustomerId = customers[0].Id,

                Description = "Customer1-Purchase2"         

            },

            new Purchase() {

                Id = Guid.NewGuid().ToString(),

                CustomerId = customers[1].Id,

                Description = "Customer2-Purchase1"         

            },

            new Purchase() {

                Id = Guid.NewGuid().ToString(),

                CustomerId = customers[1].Id,

                Description = "Customer2-Purchase2"         

            }

        };

        var purchaseItems = new List<PurchaseItem>() 

        {

            new PurchaseItem() {                

                Id = Guid.NewGuid().ToString(),

                PurchaseId= purchases[0].Id,

                Detail = "Purchase1-PurchaseItem1"          

            },

            new PurchaseItem() {                

                Id = Guid.NewGuid().ToString(),

                PurchaseId= purchases[1].Id,

                Detail = "Purchase2-PurchaseItem1"          

            },

            new PurchaseItem() {                

                Id = Guid.NewGuid().ToString(),

                PurchaseId= purchases[1].Id,

                Detail = "Purchase2-PurchaseItem2"          

            },

            new PurchaseItem() {                

                Id = Guid.NewGuid().ToString(),

                PurchaseId= purchases[3].Id,

                Detail = "Purchase3-PurchaseItem1"

            }

        };

        var result = from c in customers

            join p in purchases on c.Id equals p.CustomerId           // first join

            join pi in purchaseItems on p.Id equals pi.PurchaseId     // second join

        select new

        {

            c.Name, p.Description, pi.Detail

        };

        Console.WriteLine("Result");

        foreach(var resultItem in result)

        {

            Console.WriteLine($"{resultItem.Name}, {resultItem.Description}, {resultItem.Detail}");

        }

    }

    public class Customer

    {

       public string Id { get; set; } // A unique Id that identifies customer    

       public string Name  {get; set; }

    }

​

    public class Purchase

    {

       public string Id { get; set; }

       public string CustomerId {get; set; }

       public string Description { get; set; }

    }

​

    public class PurchaseItem

    {

       public string Id { get; set; }

       public string PurchaseId {get; set; }

       public string Detail { get; set; }

    }

​

​

}