Ci4

CodeIgniter 4 — Framework Reference

CodeIgniter 4 is a full-stack PHP 8+ MVC framework. It is not Laravel. Do not apply Laravel APIs, method names, or conventions here. When in doubt, check this skill and its references — not memory of another framework.

Related skills: ci4-api for REST API patterns, ci4-shield for authentication/authorization.

Reference Documents

For deep dives, read the relevant reference from references/:

Directory Structure

app/
  Config/         # All configuration classes (Routes, Database, Filters, Auth, etc.)
  Controllers/    # HTTP controllers
  Database/
    Migrations/   # Migration files (timestamped)
    Seeds/        # Seeder classes
  Filters/        # Before/after request filters
  Libraries/      # Custom libraries
  Models/         # Model classes
  Services/       # Custom service classes
  Views/          # View templates (.php)
    layouts/      # Layout templates
    partials/     # Reusable partials
public/           # Web root — index.php entry point lives here
writable/         # Cache, logs, sessions (must be writable)
tests/
vendor/
.env              # Environment config (copy from `env`)
spark             # CLI entry point

MVC Conventions — Hard Rules

1. Controllers handle HTTP — receive request, call model/service, return response. No business logic.
2. Models handle data — all database interaction lives here. No HTTP concerns.
3. Views handle display — no DB calls, no business logic. Only presentation.
4. Never call models from views. Ever.
5. Web controllers call models directly — that is standard CI4.
6. One controller = one resource. Name them descriptively (UserController, EventController).

Configuration

All config lives in app/Config/ as PHP classes (not arrays, not .ini files).

// app/Config/Database.php — DB connection
// app/Config/Routes.php   — route definitions
// app/Config/Filters.php  — filter aliases + global filters
// app/Config/App.php      — base URL, timezone, etc.

.env overrides any config value using dot-notation:

database.default.hostname = localhost
database.default.database = mydb
app.baseURL = 'http://example.com/'
CI_ENVIRONMENT = development

Routing

Defined in app/Config/Routes.php. See references/routing.md for complete reference.

$routes->get('users', 'UserController::index');
$routes->post('users', 'UserController::create');
$routes->get('users/(:num)', 'UserController::show/$1');
$routes->put('users/(:num)', 'UserController::update/$1');
$routes->delete('users/(:num)', 'UserController::delete/$1');

// Route groups
$routes->group('admin', ['namespace' => 'App\Controllers\Admin'], function ($routes) {
    $routes->get('users', 'UsersController::index');
});

// Apply filter to a route
$routes->get('dashboard', 'DashboardController::index', ['filter' => 'session']);

// Resource routes — generates full CRUD
$routes->resource('photos');

Route Placeholders

Controllers

See references/controllers.md for complete reference.

<?php
namespace App\Controllers;

use App\Controllers\BaseController;

class UserController extends BaseController
{
    public function index()
    {
        $model = new \App\Models\UserModel();
        return view('users/index', ['users' => $model->findAll()]);
    }
}

Request Data

$this->request->getGet('name');       // GET param
$this->request->getPost('email');     // POST param
$this->request->getJSON(true);        // JSON body as array
$this->request->getVar('key');        // GET + POST
$this->request->getFile('avatar');    // File upload

Validation

$rules = [
    'email' => 'required|valid_email',
    'name'  => 'required|min_length[2]|max_length[100]',
];

if (!$this->validate($rules)) {
    return redirect()->back()->withInput()->with('errors', $this->validator->getErrors());
}

Redirects

return redirect()->to('/dashboard');
return redirect()->back();
return redirect()->back()->withInput()->with('error', 'Something went wrong.');

GOTCHA: Never add PHP type hints (int $id) to overridden ResourceController methods like show($id = null). The parent signature uses $id = null — a type hint breaks the override.

Models

See references/models.md for complete reference.

<?php
namespace App\Models;

use CodeIgniter\Model;

class UserModel extends Model
{
    protected $table            = 'users';
    protected $primaryKey       = 'id';
    protected $useAutoIncrement = true;
    protected $returnType       = 'object';   // Always use 'object' (not 'array')
    protected $useSoftDeletes   = false;
    protected $protectFields    = true;
    protected $allowedFields    = ['name', 'email', 'role'];

    protected $useTimestamps = true;
    protected $createdField  = 'created_at';
    protected $updatedField  = 'updated_at';
}

CRUD

$model = new UserModel();
$user  = $model->find(1);                          // by ID
$users = $model->findAll();                         // all
$user  = $model->where('email', 'a@b.com')->first(); // where
$id    = $model->insert(['name' => 'Rob', 'email' => 'r@b.com']);
$model->update(1, ['name' => 'Robert']);
$model->delete(1);
$users = $model->paginate(20);                      // pagination
$pager = $model->pager;                             // pager for view

Query Builder

See references/query-builder.md for complete reference.

$db = \Config\Database::connect();
$builder = $db->table('users');

$builder->select('id, name, email')
    ->where('active', 1)
    ->orderBy('created_at', 'DESC')
    ->limit(10);

$rows = $builder->get()->getResult();     // array of objects
$row  = $builder->get()->getRow();        // single object

CRITICAL GOTCHAS:

• whereNull() does not exist in CI4. Use ->where('col IS NULL').
• ->select('DISTINCT col') returns wrong results. Use ->select('col')->distinct().

Views

See references/views.md for complete reference.

// Controller
return view('users/index', ['users' => $users, 'title' => 'Users']);

<!-- app/Views/users/index.php -->
<?= $this->extend('layouts/main') ?>

<?= $this->section('content') ?>
<h1><?= esc($title) ?></h1>
<?php foreach ($users as $user): ?>
    <p><?= esc($user->name) ?></p>
<?php endforeach; ?>
<?= $this->endSection() ?>

Always use esc() for output. Never use return inside a view that uses $this->extend().

Filters

See references/filters.md for complete reference.

<?php
namespace App\Filters;

use CodeIgniter\Filters\FilterInterface;
use CodeIgniter\HTTP\RequestInterface;
use CodeIgniter\HTTP\ResponseInterface;

class AuthFilter implements FilterInterface
{
    public function before(RequestInterface $request, $arguments = null)
    {
        if (!auth()->loggedIn()) {
            return redirect()->to('/login');
        }
    }

    public function after(RequestInterface $request, ResponseInterface $response, $arguments = null) {}
}

Register in app/Config/Filters.php, apply via routes:

$routes->get('admin', 'AdminController::index', ['filter' => ['session', 'group:admin']]);

Migrations

See references/database.md for complete reference.

php spark make:migration CreateUsersTable
php spark migrate

public function up(): void
{
    $this->forge->addField([
        'id'         => ['type' => 'INT', 'constraint' => 11, 'unsigned' => true, 'auto_increment' => true],
        'name'       => ['type' => 'VARCHAR', 'constraint' => 150],
        'email'      => ['type' => 'VARCHAR', 'constraint' => 255, 'unique' => true],
        'created_at' => ['type' => 'DATETIME', 'null' => true],
        'updated_at' => ['type' => 'DATETIME', 'null' => true],
    ]);
    $this->forge->addPrimaryKey('id');
    $this->forge->createTable('users');
}

Spark CLI Quick Reference

See references/spark-cli.md for complete reference.

php spark serve                          # dev server
php spark routes                         # list routes
php spark migrate                        # run migrations
php spark migrate:rollback               # rollback last batch
php spark db:seed DatabaseSeeder         # run seeder
php spark make:controller UserController # scaffold
php spark make:model UserModel           # scaffold
php spark make:migration CreateUsersTable
php spark make:filter AuthFilter
php spark cache:clear

Key Gotchas

See references/gotchas.md for the complete list and CI4 vs Laravel comparison.

1. whereNull() does not exist — use ->where('col IS NULL')
2. ->select('DISTINCT col') fails silently — use ->select('col')->distinct()
3. Never type-hint overridden ResourceController params
4. redirect() must be returned — without return it does nothing
5. insertBatch() bypasses $allowedFields — be deliberate about what you pass
6. Never use return inside a view using $this->extend()
7. View sections cannot be nested — close one before opening another
8. orLike() after where() needs groupStart()/groupEnd()
9. Model save() decides insert vs update by whether primary key is present
10. $returnType should always be 'object' — 'array' is inconsistent