Building REST APIs with PHP

# CHAPTER 12

Building REST APIs with PHP #

1. Introduction #

2. Learning Objectives #

• Define what an API is and why REST is the industry standard.

• Understand how to output JSON data from PHP.

• Build an API endpoint that handles HTTP GET and POST requests.

• Test an API using a tool like Postman.

3. Beginner-Friendly Explanation #

4. What is REST and JSON? #

• REST (Representational State Transfer): A set of rules for building APIs. It dictates that APIs should use standard HTTP methods (GET to read data, POST to create data).

• JSON (JavaScript Object Notation): The universal language of APIs. It is a lightweight text format that looks exactly like a PHP Associative Array. Every programming language on Earth knows how to read JSON.

5. Setting Up an API Endpoint (Outputting JSON) #

api/users.php

<?php
// Tell the client that this page will return JSON, not HTML
header("Content-Type: application/json");

require &#039;../db.php';

// Fetch users from the database
$stmt = $pdo->query("SELECT id, name, email FROM users");
$users = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Convert the PHP Array into a JSON string and output it
echo json_encode([
    "status" => "success",
    "data" => $users
]);
?>

*If you visit this URL in your browser, you won't see a website. You will see a wall of raw JSON text.*

6. Handling POST Requests in an API #

api/create_user.php

<?php
header("Content-Type: application/json");
header("Access-Control-Allow-Methods: POST");

require &#039;../db.php';

// Check if the request is actually a POST request
if ($_SERVER[&#039;REQUEST_METHOD'] == 'POST') {
    
    // Read the raw JSON sent by the mobile app or frontend framework
    $raw_json = file_get_contents("php://input");
    
    // Convert the JSON string into a PHP Associative Array
    $data = json_decode($raw_json, true);
    
    $name = $data[&#039;name'];
    $email = $data[&#039;email'];
    
    // Insert into database (Assume prepared statements are used here)
    $stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (?, ?)");
    
    if ($stmt->execute([$name, $email])) {
        // Send a success response back to the client
        echo json_encode(["message" => "User created successfully"]);
    }
}
?>

7. Testing APIs with Postman #

1. 3. Your PHP script connects to MySQL, fetches the users, and jsonencode()s the result.

1. 4. The React app receives the JSON, loops through it, and renders a beautiful UI list on the screen.

9. Best Practices #

• CORS (Cross-Origin Resource Sharing): By default, browsers block an API on api.com from sending data to a website on frontend.com for security reasons. You must add CORS Headers (header("Access-Control-Allow-Origin: *");) to your API to explicitly allow other domains to read your data.

10. Common Mistakes #

• Echoing Errors in an API: If a database connection fails and you use echo "Database Error"; in an API file, it will break the application. The mobile app is expecting JSON, not a plain text string! You must always return errors formatted as JSON: echo jsonencode(["status" => "error", "message" => "Database failed"]);.

• Challenge: Create an API endpoint called api/product.php?id=1. The script should check $GET['id'], find the product in a simulated array, and return the product details as JSON.

13. MCQs with Answers #

14. Interview Questions #

• Q: Explain the purpose of a REST API. Why would a company build an API rather than just serving HTML pages directly from their backend?

• Q: Describe how you would handle an incoming POST request in a PHP API that contains a JSON payload. What functions are required to parse it?

15. FAQs #

16. Summary #

17. Next Chapter Recommendation #