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RESTful APIs in CodeIgniter (CodeIgniter 4)

CodeIgniter 4 has first-class support for RESTful APIs, making it easy to build APIs using controllers, routing, validation, and proper HTTP responses.

1. What Is a RESTful API?

REST (Representational State Transfer) uses:

• HTTP methods (GET, POST, PUT, DELETE)

• Stateless requests

• JSON responses

• Proper HTTP status codes

2. API Folder Structure (Recommended)

app/
└── Controllers/
    └── Api/
        └── Users.php

3. Create a Resource Controller

php spark make:controller Api/Users --resource

This creates a controller with REST methods:

• index() → GET

• show() → GET /id

• create() → POST

• update() → PUT/PATCH

• delete() → DELETE

4. Example API Controller

namespace App\Controllers\Api;

use CodeIgniter\RESTful\ResourceController;
use App\Models\UserModel;

class Users extends ResourceController
{
    protected $modelName = 'App\Models\UserModel';
    protected $format    = 'json';

    public function index()
    {
        return $this->respond(
            $this->model->findAll()
        );
    }

    public function show($id = null)
    {
        $user = $this->model->find($id);

        if (! $user) {
            return $this->failNotFound('User not found');
        }

        return $this->respond($user);
    }
}

5. API Routes

In app/Config/Routes.php:

$routes->group('api', function($routes) {
    $routes->resource('users');
});

Endpoints:

GET    /api/users
GET    /api/users/1
POST   /api/users
PUT    /api/users/1
DELETE /api/users/1

6. Create (POST Request)

public function create()
{
    $data = $this->request->getJSON(true);

    if (! $this->model->insert($data)) {
        return $this->failValidationErrors(
            $this->model->errors()
        );
    }

    return $this->respondCreated($data);
}

7. Update (PUT / PATCH)

public function update($id = null)
{
    $data = $this->request->getJSON(true);

    if (! $this->model->update($id, $data)) {
        return $this->failValidationErrors(
            $this->model->errors()
        );
    }

    return $this->respondUpdated($data);
}

8. Delete

public function delete($id = null)
{
    if (! $this->model->find($id)) {
        return $this->failNotFound('User not found');
    }

    $this->model->delete($id);
    return $this->respondDeleted(['id' => $id]);
}

9. Validation in API

protected $validationRules = [
    'email' => 'required|valid_email'
];

10. API Authentication Options

• API Keys

• JWT (JSON Web Tokens)

• OAuth 2.0

• CodeIgniter Shield

11. HTTP Status Codes

12. Best Practices

✅ Use ResourceController
✅ Always return JSON
✅ Validate request data
✅ Use proper status codes
❌ Don’t expose sensitive data

Summary

• CodeIgniter supports REST APIs out of the box

• Resource controllers simplify CRUD APIs

• Proper routing, validation & responses

• Secure APIs using authentication