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Home Forums How to use DefaultIfEmpty() function in LINQ with C#? – MindStick
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1 Answers

Amrith Chandran
Amrith Chandran 12 Feb 2025
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DefaultIfEmpty() in LINQ (C#)

  • The DefaultIfEmpty() method in LINQ is used to return a default value when a collection is empty.
  • If the collection has elements, it remains unchanged.
  • If the collection is empty, it returns a collection with a single default value (for example, 0 for numbers, and null for reference types).

Basic Use

using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       List<int> numbers = new List<int>(); // Empty list
       var result = numbers.DefaultIfEmpty(); // Returns a collection with one element: 0
       Console.WriteLine("Result: " + string.Join(", ", result));
       // Output: Result: 0 (default int value)
   }
}

DefaultIfEmpty() with Linq to SQL

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace MyConsoleApplication
{
   class MindStickSoft
   {
       static void Main()
       {
           List<int> Numbers = new List<int> { 3, 5, 7, 2, 8, 4 };
           var filterValue = Numbers.Where(x => x > 20).DefaultIfEmpty(-1); // now value exist greater than 20;
           Console.WriteLine("Dafult value is: {0}", string.Join(',', filterValue));
           // Output: Dafult value is: -1
       }
   }
}

When to it

  • When working with queries that may return empty collections but require at least one value.
  • When aggregation functions (sum, average, etc.) are used to avoid exceptions on empty collections.
  • When a fallback/default value is provided instead of manually handling empty collections.

Also, read: What are the LINQ Single(), and SingleOrDefault() functions?

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