When should We use First() and FirstOrDefault() in Linq

In Linq, a very interesting topic is Difference between First() and FirstOrDefault(), or we can say when to use First() and when FirstOrDefault() extention methods, you can check difference between Single() and SingleOrDefaul() here.  So, Today I am going to explain these two extension method in Linq.

First()

It returns First element value from collection of elements or a sequence. It also returns first element of sequence when you specified condition. If result has no element than it will throws InvalidOperationException.     

When to use First()

When you know that result contain more than 1 element expected and you should only the first element of sequence.

FirstOrDefault()

FirstOrDefault()  is just like First() except that, if no element match the specified condition than it returns default value of underlying type of generic collection. It does not throw InvalidOperationException if no element found. But collection of element or a sequence is null than it throws an exception.

When to use FirstOrDefault()

When you know that output result contain more than 1 element and you should only the first element. Default value should be returned if no element is found.

Example

Use below example one by one to comment others.

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

namespace LinqFirstAndFirstOrDefault
{
    class Employee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string City { get; set; }
    }

    public class Program
    {

        static void Main(string[] args)
        {
            IList<Employee> employeeList = new List<Employee>(){
                new Employee() { Id = 10, Name = "Chris", City = "London" },
                new Employee() { Id=11, Name="Robert", City="London"},
                new Employee() { Id=12, Name="Mahesh", City="India"},
                new Employee() { Id=13, Name="Peter", City="US"},
                new Employee() { Id=14, Name="Chris", City="US"}
            };

            //First example

            var result1 = employeeList.First();
            // It will return the first element like  Id = 10, Name = "Chris", City = "London";

            var result2 = employeeList.First(e => e.Id == 12);
            // It will return the first element like  Id=12, Name="Mahesh", City="India";

            var result3 = employeeList.First(e => e.Name == "Chris");
            //Two records available for Name=Chris but it will return the first like  Id = 10, Name = "Chris", City = "London";

            var result4 = employeeList.First(e => e.Id == 16);
            //No element for Id=16 so, It throws an exception that Sequence contains more than one matching elemen


            //FirstOrDefault example

            var result5 = employeeList.FirstOrDefault();
            // It will return the first element like  Id = 10, Name = "Chris", City = "London";

            var result6 = employeeList.FirstOrDefault(e => e.Id == 12);
            // It will return the first element like  Id=12, Name="Mahesh", City="India";

            var result7 = employeeList.FirstOrDefault(e => e.Name == "Chris");
            //Two records available for Name=Chris but it will return the first like  Id = 10, Name = "Chris", City = "London";

            var result8 = employeeList.FirstOrDefault(e => e.Id == 16);
            //No element for Id=16 so, It return null for default;

                      
            Console.ReadLine();

        }
    }
}

Conclusion:

Today We learned what is difference between First() and FirstOrDefault() extention methods in Linq an when to use both of both of these.

I hope this post will help you. Please put your feedback using comment which  helps me to improve myself for next post. If you have any doubts please ask your doubts or query in the comment section and if you like this post, please share it with your friends. Thanks