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Difference Between "First" and "FirstOrDefault" in LINQ

In LINQ, both First and FirstOrDefault are used to retrieve the first element from a sequence (e.g., a list or an array) that satisfies a specified condition. However, they differ in their behavior when there's no matching element:

1. First

The First method returns the first element that meets the condition and assumes that such an element exists in the sequence. If no matching element is found, it throws an exception.

2. FirstOrDefault

In contrast, FirstOrDefault also returns the first matching element but doesn't throw an exception if none is found. Instead, it provides the default value for the type of elements in the sequence. For instance, it returns null for reference types and the default value (e.g., 0 for integers) for value types.

Now, let's see these differences in action with a C# code example:


using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

        // Using First
        int firstElement = numbers.First(x => x % 2 == 0); // Finding the first even number
        Console.WriteLine("First Element (First): " + firstElement);

        try
        {
            // Using First when there's no match (it will throw an exception)
            int nonExistentElement = numbers.First(x => x > 10); // No element > 10
        }
        catch (InvalidOperationException ex)
        {
            Console.WriteLine("Exception (First): " + ex.Message);
        }

        // Using FirstOrDefault
        int firstOrDefaultElement = numbers.FirstOrDefault(x => x > 10); // No element > 10, returns default value (0)
        Console.WriteLine("First Element (FirstOrDefault): " + firstOrDefaultElement);
    }
}

Output


First Element (First): 2
Exception (First): Sequence contains no matching element
First Element (FirstOrDefault): 0

In this code example, First successfully finds the first even number (2). However, when using First with a condition where there's no matching element (x > 10), it throws an exception.

On the other hand, FirstOrDefault returns the default value (0) when there's no matching element, avoiding exceptions. This can be particularly useful to prevent runtime errors when you are uncertain about the presence of a matching element.

This difference between First and FirstOrDefault is essential for handling scenarios in LINQ where you need to retrieve the first element meeting a condition while gracefully handling cases where no match is found.

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