How To Use Extensions For LINQ - C#

 

Introduction

Extension Methods are a new feature in C# 3.0, and they're simply user-made pre-defined functions. An Extension Method enables us to add methods to existing types without creating a new derived type, recompiling, or modifying the original types.

Extension Methods

• It enables us to add methods to existing types without creating a new derived type.
• It is a static method.
• It is defined in a static class.
• It uses “this” keyword to apply the extension to the particular type.
• We don’t want to compile the application. Visual Studio IntelliSense 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, I added the values to employee list as 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 a 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 the index of the object from the list using LINQ.
   

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

6. The extension methods can be implemented as 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

 

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<Employee> employees = new List<Employee>();
        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

You can download the code from GitHub. If you have doubts, feel free to post a comment. If you like this article and it is useful to you, do like, share the article & star the repository on GitHub.