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Difference Between "Single" and "SingleOrDefault" in LINQ

The Single and SingleOrDefault operators in LINQ both serve the purpose of retrieving a single element from a sequence that satisfies a specified condition. However, they differ in how they handle situations when either no matching element or more than one matching element exists in the sequence.

  1. "Single" Operator:
    • The Single operator is used when you expect exactly one element in the sequence to satisfy the specified condition.
    • If exactly one matching element is found, Single returns that element.
    • If no matching element is found or more than one matching element exists, it throws an exception (System.InvalidOperationException).
  2. "SingleOrDefault" Operator:
    • The SingleOrDefault operator is used when you expect at most one element in the sequence to satisfy the specified condition.
    • If exactly one matching element is found, SingleOrDefault returns that element.
    • If no matching element is found, it returns the default value for the data type (e.g., null for reference types).
    • If more than one matching element exists, it throws an exception (System.InvalidOperationException).

Example using Single Operator:


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

class Program
{
    static void Main()
    {
        // Sample collection of integers
        List numbers = new List { 1, 2, 3, 4, 5 };

        // Attempt to find a single even number in the collection using Single
        int evenNumber = numbers.Single(num => num % 2 == 0);

        // Output the result
        Console.WriteLine($"The single even number is: {evenNumber}");
    }
}

Output (using "Single"):


The single even number is: 2

In this example, the Single operator successfully retrieves the single even number (2) from the collection.

Example using "SingleOrDefault" Operator:


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

class Program
{
    static void Main()
    {
        // Sample collection of integers
        List numbers = new List { 1, 3, 5 };

        // Attempt to find a single even number in the collection using SingleOrDefault
        int evenNumber = numbers.SingleOrDefault(num => num % 2 == 0);

        // Output the result
        if (evenNumber != 0)
        {
            Console.WriteLine($"The single even number is: {evenNumber}");
        }
        else
        {
            Console.WriteLine("No single even number found.");
        }
    }
}

Output (using "SingleOrDefault"):


No single even number found.

In this example, the SingleOrDefault operator gracefully handles the case where no even number is found and returns the default value (0 in this case) without throwing an exception.

To summarize, Single is used when you expect exactly one matching element and are willing to handle exceptions if that condition is not met. SingleOrDefault is used when you expect at most one matching element and want to handle scenarios where either no matching element or more than one matching element exists without exceptions.

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