Convert SQL to Linq left join with null

You want to use .DefaultIfEmpty, as per this question.

var query = from p in Programs            join pl in ProgramLocations                on p.ProgramID equals pl.ProgramID into pp            from pl in pp.DefaultIfEmpty()            where pl == null            select p;

Here's a full, working example with some mock data objects:

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace LinqTest{    class LinqProgram    {        public class Program        {            public int ProgramID { get; set; }            public string ProgramName { get; set; }        }        public class ProgramLocation        {            public int ProgramLocationID { get; set; }            public int ProgramID { get; set; }            public string ProgramLocationName { get; set; }        }        public static List<Program> Programs = new List<Program>();        public static List<ProgramLocation> ProgramLocations = new List<ProgramLocation>();        static void Main(string[] args)        {            FillTestData();            var query = from p in Programs                        join pl in ProgramLocations                            on p.ProgramID equals pl.ProgramID into pp                        from pl in pp.DefaultIfEmpty()                        where pl == null                        select p;            foreach (var r in query)            {                Console.WriteLine("{0}: {1}", r.ProgramID, r.ProgramName);            }            Console.ReadLine();        }        private static void FillTestData()        {            var p = new Program()            {                ProgramID = Programs.Count + 1,                ProgramName = "Scary Lesson"            };            var pl = new ProgramLocation()            {                ProgramLocationID = ProgramLocations.Count + 1,                ProgramID = p.ProgramID,                ProgramLocationName = "Haunted House"            };            Programs.Add(p);            ProgramLocations.Add(pl);            p = new Program()            {                ProgramID = Programs.Count + 1,                ProgramName = "Terrifying Teachings"            };            pl = new ProgramLocation()            {                ProgramLocationID = ProgramLocations.Count + 1,                ProgramID = p.ProgramID,                ProgramLocationName = "Mystical Mansion"            };            Programs.Add(p);            ProgramLocations.Add(pl);            p = new Program()            {                ProgramID = Programs.Count + 1,                ProgramName = "Unassociated Program"            };            Programs.Add(p);        }    }}

Try this

  var progy = (         from u in db.ProgramLocations join b in db.Programs         on u.ProgramID equals b.ProgramID into yG          from y1 in yG.DefaultIfEmpty()          where y1 == null         select u.ProgramID        ).ToList();

You can check this post on MSDN.

Hope this works for you.

Could you use except instead?

var progy = (  from u in db.ProgramLocations  select u.ProgramID).Except(from b in db.Programs select b.ProgramID);