How to use Extensions for Linq – C#

Introduction:

In this tutorial, we will learn how to use extension methods with Linq in C# to simplify the coding. Extension Methods are a new feature in C# 3.0 and is nothing but a user made pre-defined functions. An Extension Method enables us to add methods to existing types without creating a new derived type, recompiling, or modify the original types.

Extension Methods:

1. It enable us to add methods to existing types without creating a new derived type.
2. It is a static method.
3. It is defined in a static class.
4. It uses “this” keyword to apply the extension to the particular type.
5. We don’t want to compile the application. Visual Studio intelli-sense will find the extension method immediately.

Coding Part:

1. I have created a Console application by selecting File->New Project->Console Application.
2. Then created a Model class “Employee.cs” with member variables like below.

   public class Employee
   {
    public string Name { get; set; }
    public string MobileNo { get; set; }
    public string Salary { get; set; }
   
    public string String()
    {
     return string.Format("Name:{0} MobileNo:{1} Salary:{2}", Name, MobileNo, Salary);
    }
   }

3. Then added values to employee list as like below

   static void AddEmployees()
   {
    employees.Add(new Employee() { Name = "Mushtaq", MobileNo = "9876543210", Salary = "20K" });
    employees.Add(new Employee() { Name = "Mohammed Mushtaq", MobileNo = "9876543211", Salary = "30K" });
    employees.Add(new Employee() { Name = "Mushtaq Ahmed", MobileNo = "9876543212", Salary = "20K" });
    employees.Add(new Employee() { Name = "Raj", MobileNo = "9876543213", Salary = "25K" });
   }

4. Now we will get results from list using Linq for “FirstOrDefault”, “LastOrDefault” or “IndexOf”.

   Console.WriteLine(employees.Where(x => x.Name.Contains("Mushtaq")).FirstOrDefault().String());
   Console.WriteLine(employees.Where(x => x.Name.Contains("Mushtaq")).LastOrDefault().String());
   Console.WriteLine(employees.IndexOf(employees.Where(x => x.Name.Contains("Mushtaq")).FirstOrDefault()));

   Result:
   
5. Now I have created a static class named as “LinqExtension.cs” and created extension methods for selecting “FirstOrDefault”, “LastOrDefault” and getting index of the object from list using Linq.

   public static class LinqExtension
   {
    public static T WhereFirstOrDefault(this List list, Func predicate)
    {
     return list.Where(predicate).FirstOrDefault();
    }
    public static T WhereLastOrDefault(this List list, Func predicate)
    {
     return list.Where(predicate).LastOrDefault();
    }
    public static int IndexOf(this List list, Func predicate)
    {
     return list.IndexOf(list.WhereFirstOrDefault(predicate));
    }
   }

6. The extension methods can be implemented as like the below

   Console.WriteLine(employees.WhereFirstOrDefault(x => x.Name.Contains("Mushtaq")).String());
   Console.WriteLine(employees.WhereLastOrDefault(x => x.Name.Contains("Mushtaq")).String());
   Console.WriteLine(employees.IndexOf(x => x.Name.Contains("Mushtaq")));

   Result:
   
7. The extension will return the same result. But the line of code will be less comparatively.

Full Code:

Full code implementations of extension methods.

namespace ExtensionsWithLinq
{
    class Program
    {
        static List employees = new List();
        static void Main(string[] args)
        {
            AddEmployees();

            Console.WriteLine("...Extension with Linq...");
            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get details of Mushtaq with Linq-FirstOrDefault");
            Console.WriteLine();
            Console.WriteLine(employees.Where(x => x.Name.Contains("Mushtaq")).FirstOrDefault().String());

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get details of Mushtaq with Linq-LastOrDefault");
            Console.WriteLine();
            Console.WriteLine(employees.Where(x => x.Name.Contains("Mushtaq")).LastOrDefault().String());

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get index of Mushtaq with Linq-IndexOf");
            Console.WriteLine();
            Console.WriteLine(employees.IndexOf(employees.Where(x => x.Name.Contains("Mushtaq")).FirstOrDefault()));

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get details of Mushtaq with Linq-FirstOrDefault Extension");
            Console.WriteLine();
            Console.WriteLine(employees.WhereFirstOrDefault(x => x.Name.Contains("Mushtaq")).String());

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get details of Mushtaq with Linq-LastOrDefault Extension");
            Console.WriteLine();
            Console.WriteLine(employees.WhereLastOrDefault(x => x.Name.Contains("Mushtaq")).String());

            Console.WriteLine();
            Console.WriteLine();
            Console.WriteLine("Linq to get index of Mushtaq with Linq-IndexOf Extension");
            Console.WriteLine();
            Console.WriteLine(employees.IndexOf(x => x.Name.Contains("Mushtaq")));

            Console.ReadLine();
        }

        static void AddEmployees()
        {
            employees.Add(new Employee() { Name = "Mushtaq", MobileNo = "9876543210", Salary = "20K" });
            employees.Add(new Employee() { Name = "Mohammed Mushtaq", MobileNo = "9876543211", Salary = "30K" });
            employees.Add(new Employee() { Name = "Mushtaq Ahmed", MobileNo = "9876543212", Salary = "20K" });
            employees.Add(new Employee() { Name = "Raj", MobileNo = "9876543213", Salary = "25K" });
        }
    }
}

Reference:

Linq	https://docs.microsoft.com/en-us/dotnet/csharp/linq/
Extensions	https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/extension-methods

Download Code

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