CodeIgniter

**Essential Configuration:**

**1. Environment Configuration (.env):**
```env
# Environment
CI_ENVIRONMENT = production # development, testing, production

# Base URL
app.baseURL = 'https://yourdomain.com/'

# Database
database.default.hostname = localhost
database.default.database = mydb
database.default.username = dbuser
database.default.password = secure_password
database.default.DBDriver = MySQLi
database.default.DBPrefix =

# Encryption
encryption.key = your-encryption-key-here # Generate: php spark key:generate
```

**2. Routes Configuration (app/Config/Routes.php):**
```php
<?php
$routes->get('/', 'Home::index');
$routes->get('blog', 'Blog::index');
$routes->get('blog/(:segment)', 'Blog::view/$1');

// RESTful API routes
$routes->resource('api/users');

// Group routes
$routes->group('admin', ['filter' => 'auth'], function($routes) {
$routes->get('dashboard', 'Admin\Dashboard::index');
$routes->resource('posts');
});
```

**3. Database Configuration (app/Config/Database.php):**
```php
<?php
public $default = [
'DSN' => '',
'hostname' => 'localhost',
'username' => 'root',
'password' => '',
'database' => 'mydb',
'DBDriver' => 'MySQLi',
'DBPrefix' => '',
'pConnect' => false,
'DBDebug' => true,
'charset' => 'utf8mb4',
'DBCollat' => 'utf8mb4_general_ci',
];
```

**4. Controller Example:**
```php
<?php
namespace App\Controllers;

class Blog extends BaseController
{
protected $blogModel;

public function __construct()
{
$this->blogModel = model('BlogModel');
}

public function index()
{
$data = [
'posts' => $this->blogModel->paginate(10),
'pager' => $this->blogModel->pager
];

return view('blog/index', $data);
}

public function view($slug)
{
$post = $this->blogModel->where('slug', $slug)->first();

if (!$post) {
throw \CodeIgniter\Exceptions\PageNotFoundException::forPageNotFound();
}

return view('blog/view', ['post' => $post]);
}
}
```

**5. Model Example with Validation:**
```php
<?php
namespace App\Models;

use CodeIgniter\Model;

class BlogModel extends Model
{
protected $table = 'posts';
protected $primaryKey = 'id';
protected $allowedFields = ['title', 'slug', 'body', 'author_id'];
protected $useTimestamps = true;

protected $validationRules = [
'title' => 'required|min_length[3]|max_length[255]',
'slug' => 'required|is_unique[posts.slug]',
'body' => 'required'
];

protected $validationMessages = [
'title' => [
'required' => 'Title is required',
'min_length' => 'Title must be at least 3 characters'
]
];
}
```

**6. Form Validation:**
```php
<?php
// In controller
public function create()
{
$validation = \Config\Services::validation();

$validation->setRules([
'email' => 'required|valid_email|is_unique[users.email]',
'password' => 'required|min_length[8]',
'confirm' => 'required|matches[password]'
]);

if (!$validation->withRequest($this->request)->run()) {
return view('register', ['validation' => $validation]);
}

// Save user
}
```

**7. Working with Database (Query Builder):**
```php
<?php
// Select
$users = $db->table('users')
->select('id, name, email')
->where('status', 'active')
->orderBy('name', 'ASC')
->get()
->getResultArray();

// Insert
$data = ['name' => 'John', 'email' => 'john@example.com'];
$db->table('users')->insert($data);

// Update
$db->table('users')
->where('id', 1)
->update(['status' => 'inactive']);

// Delete
$db->table('users')->where('id', 1)->delete();

// Join
$results = $db->table('posts')
->join('users', 'users.id = posts.author_id')
->get()
->getResult();
```

**8. Sessions and Authentication:**
```php
<?php
// Start session
$session = session();

// Set session data
$session->set('user_id', 123);
$session->set('logged_in', true);

// Get session data
$userId = $session->get('user_id');

// Flash data (available only on next request)
$session->setFlashdata('success', 'Login successful!');

// Destroy session
$session->destroy();
```

**9. Caching:**
```php
<?php
$cache = \Config\Services::cache();

// Save to cache
$cache->save('user_123', $userData, 3600); // 1 hour

// Get from cache
$data = $cache->get('user_123');

// Delete from cache
$cache->delete('user_123');

// Clear all cache
$cache->clean();
```

**10. CLI Commands (Spark):**
```bash
# Run migrations
php spark migrate

# Rollback migrations
php spark migrate:rollback

# Create migration
php spark make:migration CreateUsersTable

# Create controller
php spark make:controller Blog

# Create model
php spark make:model BlogModel

# Run seeder
php spark db:seed UserSeeder

# Clear cache
php spark cache:clear
```

**Best Practices:**
- Use environment variables for sensitive configuration
- Enable CSRF protection in production
- Use password_hash() for passwords (built-in with shield library)
- Validate and sanitize all user inputs
- Use prepared statements (Query Builder does this automatically)
- Keep writable/ directory outside document root in production
- Enable error logging and disable error display in production
- Use migrations for database schema management
- Implement proper error handling and logging
- Use caching for frequently accessed data