using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        LeftOuterJoinExample();

    }

    public static void LeftOuterJoinExample()

        {

            Person magnus = new Person { Id= 1,  FirstName = "Magnus", LastName = "Hedlund" };

            Person terry = new Person { Id = 2, FirstName = "Terry", LastName = "Adams" };

            Person charlotte = new Person { Id = 3, FirstName = "Charlotte", LastName = "Weiss" };

            Person arlene = new Person { Id = 4, FirstName = "Arlene", LastName = "Huff" };

​

            Pet barley = new Pet { Id = 1, Name = "Barley", Owner = terry };

            Pet boots = new Pet { Id = 2, Name = "Boots", Owner = terry };

            Pet whiskers = new Pet { Id = 3, Name = "Whiskers", Owner = charlotte };

            Pet bluemoon = new Pet { Id = 4, Name = "Blue Moon", Owner = terry };

            Pet daisy = new Pet { Id = 5, Name = "Daisy", Owner = magnus };

​

            // Create two lists.

            List<Person> people = new List<Person> { magnus, terry, charlotte, arlene };

            List<Pet> pets = new List<Pet> { barley, boots, whiskers, bluemoon, daisy };

​

            var query = from person in people

                        join pet in pets on person.Id equals pet.OwnerId into gj

                        from subpet in gj.DefaultIfEmpty()

                        group person by person.Id into temp1

                        select temp1.First();

        Console.WriteLine(string.Format("query count: {0}", query.Count()));

        var query1 = from person in people

                        join pet in pets on person.Id equals pet.OwnerId into gj

                        from subpet in gj.DefaultIfEmpty()

                        select person;

        Console.WriteLine(string.Format("query count no grouping: {0}", query1.Count()));

        }

}

​

class Person

    {

        public int Id { get; set; }

        public string FirstName { get; set; }

        public string LastName { get; set; }

    }

​

    class Pet

    {

        public int Id { get; set; }

        public int? OwnerId { get; set; }

        public string Name { get; set; }

        private Person _ownerPerson;

​

        public Person Owner

        {

            get { return _ownerPerson; }

            set

            {

                _ownerPerson = value;

                OwnerId = value.Id;

            }

        }

​

    }