C# Program to Join Multiple Data Sources using LINQ - GeeksforGeeks

06 Dec, 2021
LINQ is known as Language Integrated Query and it is introduced in .NET 3.5. It provides the ability to .NET languages to create queries to retrieve data from the data source. In this article, we will discuss how to join multiple data sources using LINQ. Here data source means list. So we are using list collection to create three data sources with student details, then join the data based on id, which is common in all the lists using the join keyword.
Syntax:
from iterator1 in data1
join iterator2 in data2
on iterator1.column_name equals iterator2.column_name
join iterator3 in data3
on iterator1.column_name equals iterator3.column_name
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join iteratorn in datan
on iterator1.column_name equals iteratorn.column_name
Where data is the list of the data source and iterator is used to get the data from the particular data source
Return: It will return the matching rows based on the column_names compared.
Example:
Input:

Student
new Student{id = 7058, name = "sravan kumar", dept_id = 1, add_id = 21},
new Student{id = 7059, name = "jyothika", dept_id = 2, add_id = 22},
new Student{id = 7072, name = "harsha", dept_id = 1, add_id = 22},
new Student{id = 7076, name = "khyathi", dept_id = 4, add_id = 27},
   
Department
new Department{dept_id = 1, dept_name = "CSE"},
new Department{dept_id = 2, dept_name = "CSE"},
new Department{dept_id = 3, dept_name = "IT"},  
 
Address
new Address{add_id = 21, address_name = "hyd"},
new Address{add_id = 22, address_name = "railu-peta"},
new Address{add_id = 24, address_name = "chenchu-peta"},
             
Output:
ID: 7058--> Name: sravan kumar--> Department: CSE--> Address: hyd
ID: 7059--> Name: jyothika--> Department: CSE--> Address: railu-peta
ID: 7072--> Name: harsha--> Department: CSE--> Address: railu-peta
1. Create three data sources by using a list named Student, Department, and Address by declaring the variables.
2. Add values to these lists.
3. Perform the join based on student id, department id, and address id.
var result = (from stu in students

join dept in departments on stu.dept_id equals dept.dept_id

join add in addresses on stu.add_id equals add.add_id).ToList();
4. Select the data using select() method.
select new
{
    ID = stu.id,
    Name = stu.name,
    DeptName = dept.dept_name,
    address = add.address_name
}
5. Display using for each loop.
foreach (var e in result)
{
    Console.WriteLine("\tID: " + e.ID + "--> Name: " + 
                               e.Name + "--> Department: " + 
                           e.DeptName + "--> Address: " + e.address);
}
Example:
C#
// C# program to join multiple data sources// Using LINQusing System;using System.Linq;using System.Collections.Generic;  // Variables for Student listpublic class Student{    public int id;    public string name;    public int dept_id;    public int add_id;}  // Variables for Department listpublic class Department{    public int dept_id;    public string dept_name;}  // Variables for Address listpublic class Address {    public int add_id;    public string address_name;}  class GFG{  // Driver code   static void Main(string[] args){          // Enter data for Student list    List<Student> students = new List<Student>()    {        new Student{ id = 7058, name = "sravan kumar",                     dept_id = 1, add_id = 21 },        new Student{ id = 7059, name = "jyothika",                     dept_id = 2, add_id = 22 },        new Student{ id = 7072, name = "harsha",                     dept_id = 1, add_id = 22 },        new Student{ id = 7076, name = "khyathi",                     dept_id = 4, add_id = 27 },    };      List<Department> departments = new List<Department>()    {        new Department{ dept_id = 1, dept_name = "CSE" },        new Department{ dept_id = 2, dept_name = "CSE" },        new Department{ dept_id = 3, dept_name = "IT " },    };      List<Address> addresses = new List<Address>()    {        new Address{ add_id = 21, address_name = "hyd" },        new Address{ add_id = 22, address_name = "railu-peta" },        new Address{ add_id = 24, address_name = "chenchu-peta" },    };      // Join the students and other two tables    var result = (from stu in students                  join dept in departments on stu                .dept_id equals dept                .dept_id                                  join add in addresses on stu                .add_id equals add.add_id                                  select new                 {                    ID = stu.id, Name = stu.name,                    DeptName = dept.dept_name,                    address = add.address_name                                       }).ToList();                      // Display the result    foreach(var e in result)    {        Console.WriteLine("\tID: " + e.ID + "--> Name: " +                                    e.Name + "--> Department: " +                                e.DeptName + "--> Address: " + e.address);    }}}
Output:
ID: 7058--> Name: sravan kumar--> Department: CSE--> Address: hyd
ID: 7059--> Name: jyothika--> Department: CSE--> Address: railu-peta
ID: 7072--> Name: harsha--> Department: CSE--> Address: railu-peta
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