Fórum ➡ GroupJoin ➡ Join ➡ Easily ‼, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

// aljodav
// http://rextester.com/users/376

namespace Rextester
{
    class Lead{public int Id;public string Name,Phone,Address;}
    class LeadProg{public int Id,PrgId;}
    class Prog{public int PrgId;public string Prg;}
    class Program
    {
        static IEnumerable<Prog> GetProgs(){
            return new List<Prog>{
                new Prog{PrgId=1,Prg="A qwe"},
                    new Prog{PrgId=2,Prg="B asd"}, 
                    new Prog{PrgId=3,Prg="C zxc"},
                    new Prog{PrgId=4,Prg="D rty"}, 
                    new Prog{PrgId=1,Prg="E fgh"},
                    new Prog{PrgId=2,Prg="F vbn"}, 
                    new Prog{PrgId=3,Prg="G poi"},
                    new Prog{PrgId=1,Prg="H lkj"},
                    new Prog{PrgId=2,Prg="I mnb"}, 
                    new Prog{PrgId=1,Prg="J qaz"},
                    new Prog{PrgId=5,Prg="K wsx"},
                    new Prog{PrgId=6,Prg="L edc"},
            };
        }
        static IEnumerable<LeadProg> GetLeadProgs(){
            return new List<LeadProg>{
                new LeadProg{Id=1,PrgId=3},
                    new LeadProg{Id=2,PrgId=12345}, 
                    new LeadProg{Id=3,PrgId=1},
                    new LeadProg{Id=4,PrgId=4},
                    new LeadProg{Id=5,PrgId=6},
                    new LeadProg{Id=6,PrgId=5},
                    new LeadProg{Id=7,PrgId=2},
            };
        }
        static IEnumerable<Lead> GetLeads(){
            return new List<Lead>{
                new Lead{Id=1,Name="mae",Phone="999",Address="Qwe St"},
                    new Lead{Id=2,Name="ray",Phone="888",Address="Rty St"},
                    new Lead{Id=3,Name="ann",Phone="777",Address="Asd St"},
                    new Lead{Id=4,Name="jim",Phone="666",Address="Fgh St"},
                    new Lead{Id=5,Name="kim",Phone="555",Address="Zxc St"},
                    new Lead{Id=6,Name="tim",Phone="444",Address="Vbn St"},
                    new Lead{Id=7,Name="may",Phone="333",Address="Zaq St"},
            };
        }
        
        public static void Main(string[] args)
        {
            IEnumerable<LeadProg> outer=GetLeadProgs();
            IEnumerable<Prog> inner1=GetProgs();
            IEnumerable<Lead> inner2=GetLeads();
            
            Console.WriteLine("LeadId  Name  Phone  Address  ( Programs below )\n");
            
            outer
                .GroupJoin(
                    inner1,
                    lead=>lead.PrgId,
                    prg=>prg.PrgId,
                    (lead,prgs)=>new{
                        LeadId=lead.Id,
                        Programs=prgs.Select(x=>x.Prg)
                    })
                .Join(
                    inner2,
                    groupjoin=>groupjoin.LeadId,
                    lead=>lead.Id,
                    (groupjoin,lead)=>new{
                        LeadId=lead.Id,
                        Name=lead.Name,
                        Phone=lead.Phone,
                        Address=lead.Address,
                        Programs=groupjoin.Programs
                    })
                .ToList()
                .ForEach(x=>{
                    Console.WriteLine("\n{0,6}  {1,-4}  {2,-5}  {3}\n",x.LeadId,x.Name,x.Phone,x.Address);
                    foreach(string y in x.Programs){
                        Console.WriteLine("\t{0}",y);
                    }
                });
            
            Console.WriteLine("\n\nHello, world!");
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,17 sec, absolute running time: 0,11 sec, cpu time: 0,11 sec, average memory usage: 17 Mb, average nr of threads: 4