020 LINQ Left Outer Join

Left outer join return all element of the first collection,does not matter whether it has any correlated elements in the second collection.You can implement LINQ left outer join by applying the DefaultIfEmpty method on the results of a group join.

Here is the example of left outer join using LINQ.
Example
---------------------------------------------------

using System;

using System.Collections.Generic;

using System.Data.SqlClient;

using System.Data.Sql;

using System.Data;

using System.Linq;

using System.Collections;

using System.Xml;

using System.Xml.Linq;

using System.IO;

namespace ConsoleApplication1

{

        class Program

        {

           static void Main(string[] args)

           {

                    var students = new student[]

                     {

                           new student{name = "John1",roll=123,age=12},

                           new student{name = "John2",roll=124,age=13},

                           new student{name = "John3",roll=125,age=14},

                           new student{name = "John4",roll=126,age=15},

                           new student{name = "John5",roll=127,age=16},

                           new student{name = "John6",roll=128,age=17},

                           new student{name = "John7",roll=129,age=18}

                   };

                  var students2 = new student2[]

                  {

                      new student2{address = "12,ABC Road",roll=123,age=12},

                      new student2{address = "13,ABC Road",roll=124,age=13},

                      new student2{address = "14,ABC Road",roll=125,age=14},

                      new student2{address = "15,ABC Road",roll=126,age=15},

                     new student2{address = "16,ABC Road",roll=132,age=16},

                     new student2{address = "17,ABC Road",roll=133,age=17},

                     new student2{address = "18,ABC Road",roll=134,age=17}

                };

                       var query = from a in students

                                           join b in students2 on a.roll equals b.roll into dep

                                            from c in dep.DefaultIfEmpty()

                                            select new

                                           {

                                              a.name,

                                              a.roll,

                                              a.age,

                                              c.address

                                          };

                                    foreach (var obj in query)

                                    {

                                        Console.WriteLine("Name :{0} Roll : {1} Age:{2} Address : {3}", obj.name, obj.roll, obj.age, obj.address);

                                    }

                               Console.ReadKey();

                    }

          }

}

public class student

{

          public string name { get; set; }

          public int roll { get; set; }

          public int age { get; set; }

}

public class student2

{

          public string address { get; set; }

          public int roll { get; set; }

          public int age { get; set; }

}

Output :

Name :John1 Roll : 123 Age:12 Address : 12,ABC Road
Name :John2 Roll : 124 Age:13 Address : 13,ABC Road
Name :John3 Roll : 125 Age:14 Address : 14,ABC Road
Name :John4 Roll : 126 Age:15 Address : 15,ABC Road

Here is the example of left outer join using Group join.

Example
----------------------------------------------

using System;

using System.Collections.Generic;

using System.Data.SqlClient;

using System.Data.Sql;

using System.Data;

using System.Linq;

using System.Collections;

using System.Xml;

using System.Xml.Linq;

using System.IO;

namespace ConsoleApplication1

{

          class Program

          {

                 static void Main(string[] args)

                 {

                          var students = new student[]

                                 {

                                     new student{name = "John1",roll=123,age=12},

                                     new student{name = "John2",roll=124,age=13},

                                     new student{name = "John3",roll=125,age=14},

                                     new student{name = "John4",roll=126,age=15},

                                     new student{name = "John5",roll=127,age=16},

                                     new student{name = "John6",roll=128,age=17},

                                     new student{name = "John7",roll=129,age=18}

                               };

                         var students2 = new student2[]

                             {

                                    new student2{address = "12,ABC Road",roll=123,age=12},

                                    new student2{address = "13,ABC Road",roll=124,age=13},

                                    new student2{address = "14,ABC Road",roll=125,age=14},

                                    new student2{address = "15,ABC Road",roll=126,age=15},

                                    new student2{address = "16,ABC Road",roll=132,age=16},

                                    new student2{address = "17,ABC Road",roll=133,age=17},

                                    new student2{address = "18,ABC Road",roll=134,age=17}

                            };

var query = students.GroupJoin(students2, lang => lang.roll, pers => pers.roll,

(lang, ps) => new { Name = lang.name, Roll = lang.roll, Age = lang.age, Persons = ps });

foreach (var obj in query)

{

            Console.WriteLine("Name :{0} ", obj.Name);

}

              Console.ReadKey();

               }

         }

}

public class student

{

           public string name { get; set; }

           public int roll { get; set; }

           public int age { get; set; }

}

public class student2

{

        public string address { get; set; }

        public int roll { get; set; }

        public int age { get; set; }

}

Output 

Name :John1
Name :John2
Name :John3
Name :John4
Name :John5
Name :John6
Name :John7