Introducing a Service Layer in a PHP Application

A service layer contains application use cases between controllers and persistence abstractions.

What It Does and When to Use It

Separate business logic, input handling and rendering at a clearly identified boundary. Controllers translate HTTP input to operations; domain services implement rules; templates render escaped output.

Requirements, Inputs and Expected Behavior

Confirm the runtime, extension, environment variables, and permissions before running the examples in production. Avoid making services merely pass-through wrappers with no behavior.

Example 1: Basic Operation

Separate business logic, input handling and rendering at a clearly identified boundary.

<?php
final class OrderService { public function __construct(private PDO $pdo) {} public function countOrders(): int { return (int)$this->pdo->query('SELECT COUNT(*) FROM orders')->fetchColumn(); } }
// The controller delegates business operations to OrderService.

Example 2: Behavior and Validation

Use the front controller to select responses while keeping routing separate from models.

<?php
$path=parse_url($_SERVER['REQUEST_URI']??'/',PHP_URL_PATH);
if ($path==='/health') { header('Content-Type: application/json'); echo json_encode(['status'=>'ok']); }
else { http_response_code(404); echo 'Not found'; }

Practical Example: Application Use

Render a trusted template path with controlled data; never derive template paths from user input.

<?php
function render(string $template, array $data): string {
    extract($data, EXTR_SKIP); ob_start();
    try { require $template; return (string)ob_get_clean(); }
    catch(Throwable $e) { ob_end_clean(); throw $e; }
}

Important Behavior and Edge Cases

The second example highlights: Use the front controller to select responses while keeping routing separate from models. The practical example adds: Render a trusted template path with controlled data; never derive template paths from user input.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• A service layer contains application use cases between controllers and persistence abstractions.
• Render a trusted template path with controlled data; never derive template paths from user input.
• Treat template names, route parameters and user data as separate trust domains.