LINQ Group Join

In LINQ, a Join clause with an 'into' expression is called a Group join. In LINQ, Group join produces a sequence of the elements of the objects, which is based on the matching element from both left and right collections.

In case, if no matching element found from the right collection with the left collection, then the join clause will return an empty array. In LINQ, Group join is an equivalent to inner equi join except for the result of the elements organized into groups.

Syntax of LINQ Group Join

The syntax of using the LINQ Group Join to get the matching element from the given collections based on our requirement.

var result = from d in objDept
join e in objEmp on d.DepId equals e.DeptId into empDept
select new
{
    DepartmentName = d.DepName,
    Employees = from emp2 in empDept
    orderby emp2.Name
     select emp2
};

From the above syntax, we used a Join clause with an 'into' expression to get the matching elements from the collections.

Examples of LINQ Group Join

Here is the example of LINQ Group Join to get the matching elements from the collections based on the required conditions.

using System;
using System. Collections;
using System.Collections.Generic;
using System. Linq;
using System. Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Programme2
    {
        static void Main(string[] args)
        {
`//Create an object 'objDept1' and add some values in the list of the 'Department'
            List<Department> objDept1 = new List<Department>
    (){
    //insert the data in the Department class
    new Department{DepId=1,DepName="Software"},
    new Department{DepId=2,DepName="Finance"},
    new Department{DepId=3,DepName="Health"}
    };
    //Create an object 'objEmp1' and add some values in the list of the 'Employee'
    List<Employee>objEmp1 = new List<Employee>()
            {
    //add the data in the Employee class
            new Employee { EmpId=1,Name = "Devansh", DeptId=1 },
            new Employee { EmpId=2,Name = "Shubham", DeptId=1 },
            new Employee { EmpId=3,Name = "Aman", DeptId=2 },
            new Employee { EmpId=4,Name = "Raman", DeptId =2},
            new Employee { EmpId=5,Name = "Madhav"}
            };
    //used the linq queries to group the elements of both the table by using the join clause based on the name of the department
            var result = from d in objDept1
            join e in objEmp1 on d.DepId equals e.DeptId into empDept
            select new
            {
            DepartmentName = d.DepName,
            Employees = from emp2 in empDept
            orderby emp2.Name
            select emp2
            };
            int totalItems = 0;
            foreach (var empGroup in result)
            {
            Console.WriteLine(empGroup.DepartmentName);
            foreach (var item in empGroup.Employees)
            {
            totalItems++;
            Console.WriteLine("    {0}", item.Name);
            }
            }
            Console.ReadLine();
            }
            }
    //create the class Department and Employee having the different information
            class Department
            {
            public int DepId { get; set; }
            public string DepName { get; set; }
            }
            class Employee
            {
            public int EmpId { get; set; }
            public string Name { get; set; }
            public int DeptId { get; set; }
            }
            }

In the above example, we used the Join clause with an 'into' expression, and we are grouping the elements based on the department name.

Output: