Custom validation rules in Laravel - Mini Project: Build & Apply

Laravel Custom Validation Rules

📖 Scenario: You are building a simple Laravel form to register users. You want to ensure the username is unique and only contains letters and numbers.

🎯 Goal: Create a custom validation rule in Laravel that checks if a username contains only letters and numbers, then apply it to a form request.

📋 What You'll Learn

Create a custom validation rule class named AlphaNumOnly

Add a passes method that returns true only if the username contains letters and numbers

Add a message method that returns a custom error message

Use the custom rule in a form request validation for the username field

💡 Why This Matters

🌍 Real World

Custom validation rules help enforce specific business logic on user input beyond built-in rules, improving data quality and user experience.

💼 Career

Laravel developers often create custom validation rules to meet unique application requirements and maintain clean, reusable validation code.

1

Create the custom validation rule class

Create a Laravel custom validation rule class named AlphaNumOnly using the artisan command php artisan make:rule AlphaNumOnly.

Laravel

# Run the artisan command to create the rule class
# Your code here

Hint

Use the artisan command to create the rule class, then implement passes and message methods.

2

Add a form request class for user registration

Create a Laravel form request class named RegisterUserRequest using the artisan command php artisan make:request RegisterUserRequest.

Laravel

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;

class AlphaNumOnly implements Rule
{
    public function passes($attribute, $value)
    {
        return preg_match('/^[a-zA-Z0-9]+$/', $value) === 1;
    }

    public function message()
    {
        return 'The :attribute may only contain letters and numbers.';
    }
}

// Create the RegisterUserRequest class using artisan
# Your code here

Hint

Use the artisan command to create the form request class.

3

Add validation rules to the form request

In the RegisterUserRequest class, add a rules method that returns an array with the username field using the required, unique:users,username, and the custom AlphaNumOnly rule.

Laravel

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;

class AlphaNumOnly implements Rule
{
    public function passes($attribute, $value)
    {
        return preg_match('/^[a-zA-Z0-9]+$/', $value) === 1;
    }

    public function message()
    {
        return 'The :attribute may only contain letters and numbers.';
    }
}

// Command run in terminal:
// php artisan make:request RegisterUserRequest

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;
use App\Rules\AlphaNumOnly;

class RegisterUserRequest extends FormRequest
{
    public function authorize()
    {
        return true;
    }

    public function rules()
    {
        // Add validation rules here
        # Your code here
    }
}

Hint

Return an array with the username key and the required validation rules including the custom rule.

4

Use the form request in the controller

In your UserController, update the store method to accept the RegisterUserRequest as a parameter and use it to validate the incoming request.

Laravel

 ['required', 'unique:users,username', new AlphaNumOnly()],
        ];
    }
}

namespace App\Http\Controllers;

use App\Http\Requests\RegisterUserRequest;

class UserController extends Controller
{
    public function store(RegisterUserRequest $request)
    {
        // Add code to create user with validated data
        # Your code here
    }
}

Hint

Use the form request as a parameter and call User::create with the validated data.

Practice

1. What is the main purpose of creating a custom validation rule in Laravel?

easy

A. To define your own logic for validating data beyond built-in rules

B. To change the database schema automatically

C. To create new database tables

D. To generate HTML forms automatically

Solution

1. Step 1: Understand Laravel validation rules

   Laravel provides built-in rules but sometimes you need to check data in a way not covered by them.

2. Step 2: Purpose of custom validation rules

   Custom rules let you write your own logic to validate data exactly as you want.

3. Final Answer:

   To define your own logic for validating data beyond built-in rules -> Option A

4. Quick Check:

   Custom validation = custom logic [OK]

Hint: Custom rules check data your way, not Laravel's default [OK]

Common Mistakes:

• Thinking custom rules change database structure
• Confusing validation with form generation
• Assuming custom rules create tables

2. Which method must you implement in a Laravel custom validation rule class to check if the data passes validation?

easy

A. check

B. message

C. validate

D. passes

Solution

1. Step 1: Recall custom rule methods

   Laravel custom validation rules require two methods: passes and message.

2. Step 2: Identify method for validation logic

   The passes method contains the logic to decide if the data is valid or not.

3. Final Answer:

   passes -> Option D

4. Quick Check:

   passes() checks data validity [OK]

Hint: passes() returns true/false for validation [OK]

Common Mistakes:

• Using message() to check data validity
• Assuming validate() or check() are required methods
• Confusing method names

3. Given this custom rule class snippet, what will $rule->passes('age', 17) return?

class AdultRule implements \Illuminate\Contracts\Validation\Rule {
    public function passes($attribute, $value) {
        return $value >= 18;
    }
    public function message() {
        return 'You must be an adult.';
    }
}

medium

A. true

B. Throws an error

C. false

D. null

Solution

1. Step 1: Understand the passes method logic

   The method returns true if the value is 18 or more, false otherwise.

2. Step 2: Evaluate passes with value 17

   Since 17 is less than 18, the method returns false.

3. Final Answer:

   false -> Option C

4. Quick Check:

   17 < 18 means passes() = false [OK]

Hint: Check condition in passes() with given value [OK]

Common Mistakes:

• Assuming 17 passes as adult
• Thinking passes() throws error for numbers
• Confusing message() with passes()

4. What is wrong with this custom validation rule class?

class EvenNumberRule implements \Illuminate\Contracts\Validation\Rule {
    public function passes($attribute, $value) {
        return $value % 2 == 0
    }
    public function message() {
        return 'The number must be even.';
    }
}

medium

A. message method should return a boolean

B. Missing semicolon after return statement in passes method

C. passes method should accept only one parameter

D. Class must extend a base validation class

Solution

1. Step 1: Check syntax in passes method

   The return statement lacks a semicolon at the end, causing a syntax error.

2. Step 2: Verify other method signatures

   message() correctly returns a string, passes() correctly has two parameters, and implementing the interface is enough.

3. Final Answer:

   Missing semicolon after return statement in passes method -> Option B

4. Quick Check:

   Missing semicolon = syntax error [OK]

Hint: Look for missing semicolons in PHP code [OK]

Common Mistakes:

• Thinking message() must return boolean
• Assuming passes() takes one parameter
• Believing class must extend base class

5. You want to create a custom validation rule that checks if a string contains only vowels. Which approach correctly implements the passes method?

hard

A. return preg_match('/^[aeiouAEIOU]+$/', $value) === 1;

B. return strlen($value) > 0 && ctype_alpha($value);

C. return strpos($value, 'aeiou') !== false;

D. return $value == strtolower($value);

Solution

1. Step 1: Understand the requirement

   The string must contain only vowels (a, e, i, o, u) in any case.

2. Step 2: Analyze each option

   return preg_match('/^[aeiouAEIOU]+$/', $value) === 1; uses regex to check if the string contains only vowels from start to end. return strlen($value) > 0 && ctype_alpha($value); checks only letters but not vowels. return strpos($value, 'aeiou') !== false; checks if 'aeiou' substring exists, which is incorrect. return $value == strtolower($value); checks if string is lowercase, unrelated to vowels.

3. Final Answer:

   return preg_match('/^[aeiouAEIOU]+$/', $value) === 1; -> Option A

4. Quick Check:

   Regex matching only vowels = correct passes() [OK]

Hint: Use regex to match only vowels in string [OK]

Common Mistakes:

• Using ctype_alpha without vowel check
• Checking substring instead of full string
• Confusing case check with vowel check