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Home Forums Explain First(), FirstOrDefault() function in LINQ with C#. – MindStick
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1 Answers

Ashutosh Patel
Ashutosh Patel 12 Feb 2025
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First() vs FirstOrDefault() in LINQ (C#)


Both First() and FirstOrDefault() are used to retrieve the first element from a collection, but they behave differently when no matching element is found.

First()

  • Returns the first element in the collection that matches a given condition.
  • Throws an exception (InvalidOperationException) if no element is found.
  •  

Example-

find the first even number in the list,
 

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       List<int> numbers = new List<int> { 3, 7, 8, 10, 15 };
       int firstEven = numbers.First(n => n % 2 == 0);
       Console.WriteLine("First Even Number: " + firstEven);
       // Output: First Even Number: 8
   }
}

Example (Throws Exception)

List<int> numbers = new List<int> { 1, 3, 5, 7 };
int firstEven = numbers.First(n => n % 2 == 0); // No even number exist.
// Throws: InvalidOperationException: "Sequence contains no matching element"

FirstOrDefault()

  • Returns the first matching element, or the default value (null for reference types, 0 for numeric types) if no element is found.
  • Does not throw an exception when no element matches.

Example-

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       List<int> numbers = new List<int> { 3, 7, 8, 10, 15 };
       int firstEven = numbers.FirstOrDefault(n => n % 2 == 0);
       Console.WriteLine("First Even Number: " + firstEven);
       // Output: First Even Number: 0 (if no even number exists)

       // Example with Strings
       List<string> names = new List<string> { "Alice", "Bob", "Charlie" };
       string result = names.FirstOrDefault(n => n.StartsWith("Z"));
       Console.WriteLine(result == null ? "No match found" : result);
       // Output: No match found
   }
}

When to Use What?

  • When you are sure that at least one matching element exists, use First().
  • When no matching element exists, use FirstOrDefault() (to avoid exceptions).

Also, Read: LINQ Aggregate functions

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