How to Use LINQ Contains in C# - Simple Guide

Use Contains in LINQ to check if a collection has a specific item by calling collection.Contains(item). It returns true if the item exists, otherwise false. This works with lists, arrays, and other enumerable types.

Syntax

The basic syntax of LINQ Contains is:

• collection.Contains(item) - checks if item exists in collection.
• collection can be any enumerable like an array, list, or other LINQ-supported collections.
• Returns a bool: true if found, false if not.

csharp

bool result = collection.Contains(item);

Example

This example shows how to use Contains to check if a list of strings contains a specific word.

csharp

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

class Program
{
    static void Main()
    {
        List<string> fruits = new List<string> { "apple", "banana", "cherry" };
        bool hasBanana = fruits.Contains("banana");
        bool hasOrange = fruits.Contains("orange");

        Console.WriteLine($"Contains banana? {hasBanana}");
        Console.WriteLine($"Contains orange? {hasOrange}");
    }
}

Output

Contains banana? True
Contains orange? False

Common Pitfalls

Common mistakes when using Contains include:

• Using Contains on a collection of complex objects without overriding Equals and GetHashCode, which causes unexpected false results.
• Case sensitivity issues when checking strings, since Contains is case-sensitive by default.
• Confusing Contains with string method Contains which checks substrings, not collection membership.

Example of case sensitivity issue and fix:

csharp

var fruits = new List<string> { "Apple", "Banana", "Cherry" };

// Case-sensitive check (will be false)
bool hasApple = fruits.Contains("apple");

// Case-insensitive check using LINQ Any
bool hasAppleIgnoreCase = fruits.Any(f => f.Equals("apple", StringComparison.OrdinalIgnoreCase));

Quick Reference

• Purpose: Check if a collection contains an element.
• Return type: bool
• Case sensitivity: Yes, for strings.
• Works with: Arrays, Lists, IEnumerable<T>.
• Use with complex types: Override Equals and GetHashCode.

Key Takeaways

Use Contains to check if a collection has a specific item, returning true or false.

Remember Contains is case-sensitive for strings by default.

For complex objects, override Equals and GetHashCode to get correct results.

Use Any with a custom comparison for case-insensitive string checks.

Contains works on arrays, lists, and any enumerable collection.