Recap - Form Validator

Part of the Object Oriented Programming section of Coddy's PHP journey — lesson 69 of 91.

Challenge

Easy

Let's build a user registration form validator that collects validation errors and reports them all at once, rather than stopping at the first problem. This is how real-world form validation works — users want to see all issues with their submission, not fix them one at a time.

You'll organize your code across four files:

ValidationException.php — Create a base ValidationException class that extends Exception. This serves as the parent for all validation-related exceptions.
Exceptions.php — Include the ValidationException file and create three specific exception classes that extend ValidationException:
- RequiredFieldException — Accepts a field name in its constructor and passes the message "[fieldName] is required" to the parent
- InvalidEmailException — Accepts an email string in its constructor and passes the message "'[email]' is not a valid email" to the parent
- MinLengthException — Accepts a field name and a minimum length (int) in its constructor and passes the message "[fieldName] must be at least [minLength] characters" to the parent
FormValidator.php — Include the Exceptions file and create a FormValidator class with these validation methods:
- validateRequired(?string $value, string $fieldName): string — Throws RequiredFieldException if the value is null or empty (after trimming), otherwise returns the trimmed value
- validateEmail(string $email): string — Throws InvalidEmailException if the email is invalid (use filter_var with FILTER_VALIDATE_EMAIL), otherwise returns the email
- validateMinLength(string $value, string $fieldName, int $minLength): string — Throws MinLengthException if the string length is less than the minimum, otherwise returns the value
main.php — Include the FormValidator file. You'll receive three inputs: a username, an email, and a password.
Create a FormValidator and an empty array to collect error messages. Validate each field in a separate try-catch block:
- Validate username as required
- Validate email as required first, then validate it as a valid email format
- Validate password as required first, then validate it has a minimum length of 8 characters
When catching a ValidationException, add its message to your errors array instead of stopping execution.

After all validations, if there are errors, print each error message on its own line. If there are no errors, print "Registration successful".

This pattern of collecting all errors before reporting them is essential for good user experience. Your exception hierarchy makes it easy to catch all validation problems with a single catch block while still having specific exception types for different validation failures.

Try it yourself

<?php
require_once 'FormValidator.php';

// Read inputs
$username = trim(fgets(STDIN));
$email = trim(fgets(STDIN));
$password = trim(fgets(STDIN));

// Create a FormValidator instance
$validator = new FormValidator();

// Create an empty array to collect error messages
$errors = [];

// TODO: Validate username as required in a try-catch block
// Catch ValidationException and add its message to $errors array

// TODO: Validate email as required first, then validate it as a valid email format
// Use a try-catch block and add any error messages to $errors array

// TODO: Validate password as required first, then validate minimum length of 8 characters
// Use a try-catch block and add any error messages to $errors array

// TODO: After all validations:
// - If there are errors, print each error message on its own line
// - If there are no errors, print "Registration successful"

?>