php 62 lines · 9 steps

Building a reusable address form validator in PHP

A validator class accumulates field errors into a keyed map, layering required checks, format rules, and country-specific logic.

Explained by highlit

Intermediate validation error-accumulation regex conditional-logic encapsulation

1<?php
2 
3namespace App\Validation;
4 
5class AddressFormValidator
6{
  private array $errors = [];
8 
  public function validate(array $data): array
  {
      $this->errors = [];
12 
      $this->required($data, 'recipient', 'Recipient name is required.');
      $this->required($data, 'phone', 'A contact phone number is required.');
15 
      if (!empty($data['phone']) && !preg_match('/^\+?[0-9 ()-]{7,20}$/', $data['phone'])) {
          $this->add('phone', 'Phone number format is invalid.');
      }
19 
      $address = $data['address'] ?? [];
21 
      $this->requiredNested($address, 'address.line1', 'Street address is required.');
      $this->requiredNested($address, 'address.city', 'City is required.');
      $this->requiredNested($address, 'address.country', 'Country is required.');
25 
      $country = strtoupper(trim($address['country'] ?? ''));
27 
      if ($country === 'US') {
          $zip = $address['postal_code'] ?? '';
          if (!preg_match('/^\d{5}(-\d{4})?$/', $zip)) {
              $this->add('address.postal_code', 'A valid US ZIP code is required.');
          }
          if (empty($address['state'])) {
              $this->add('address.state', 'State is required for US addresses.');
          }
      } elseif ($country !== '' && empty($address['postal_code'])) {
          $this->add('address.postal_code', 'Postal code is required.');
      }
39 
      return $this->errors;
  }
42 
  private function required(array $data, string $key, string $message): void
  {
      if (trim((string) ($data[$key] ?? '')) === '') {
          $this->add($key, $message);
      }
  }
49 
  private function requiredNested(array $address, string $fullKey, string $message): void
  {
      $field = substr($fullKey, strrpos($fullKey, '.') + 1);
      if (trim((string) ($address[$field] ?? '')) === '') {
          $this->add($fullKey, $message);
      }
  }
57 
  private function add(string $key, string $message): void
  {
      $this->errors[$key][] = $message;
  }
62}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Collecting errors into a keyed map lets one pass report every problem at once instead of failing on the first.
2Small private helpers like required and add keep validation rules readable and consistent.
3Conditional branches let you apply locale-specific rules without cluttering the common path.

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