Backend Technologies · PHP
CodeIgniter — Free Learning Resources
Free, printable resources for CodeIgniter — practice problems, quick-reference cheatsheet, and an interview prep sheet. No sign-up required.
CodeIgniter — Practice Worksheet
Structured exercises and problems to build hands-on CodeIgniter skills. Work through key concepts step by step.
CodeIgniter — Cheatsheet
One-page quick-reference for CodeIgniter — key syntax, commands, patterns, and best practices at a glance.
CodeIgniter — Interview Sheet
Top CodeIgniter interview questions with concise answers. Get ready for any technical round with this focused prep sheet.
About CodeIgniter
CodeIgniter is a powerful PHP framework with a very small footprint. Known for its simplicity, speed, and near-zero configuration, it remains popular for developers who need a lightweight, well-documented framework that runs on nearly any shared hosting environment.
CodeIgniterCheat Sheet — What's Covered
- ✓MVC structure — Controllers, Models, Views, and URI routing
- ✓Query Builder for database operations without raw SQL
- ✓Form validation library and input sanitization
- ✓Session management, helpers, and libraries
- ✓CodeIgniter 4 — namespaces, PSR compliance, and CLI commands
Frequently Asked Questions — CodeIgniter
How does CodeIgniter routing work?
CodeIgniter maps URLs to controllers by convention: /user/profile calls UserController::profile(). Define custom routes in app/Config/Routes.php: $routes->get('users/(:num)', 'Users::show/$1'). CodeIgniter 4 supports named routes and resource controllers.
How does CodeIgniter's Query Builder work?
Use $db->table('users')->where('active', 1)->get()->getResult() for SELECT. It builds parameterized queries automatically, protecting against SQL injection. Also supports insert(), update(), delete(), and join() with a fluent interface.
How does form validation work in CodeIgniter?
Load the validation library: $this->validate(['username' => 'required|min_length[3]']). Rules include required, min_length, max_length, valid_email, is_unique. Check validation_errors() in the view. CodeIgniter 4 uses Services::validation().
What changed in CodeIgniter 4?
CI4 adopts PSR-4 autoloading with namespaces, requires PHP 7.4+, adds a CLI (Spark), improves the routing system, adds a proper ORM (Entities + Models), and uses a service container. It's a near-complete rewrite while retaining CI's simplicity philosophy.
How does CodeIgniter handle sessions?
Sessions are managed by CodeIgniter's Session library, supporting multiple drivers: files (default), database, Redis, and Memcached. Set session data with $session->set(['user_id' => $id]); read with $session->get('user_id'). Supports flashdata for one-request data.
Who Is This For?
PHP developers building web applications who need a simple, fast framework with minimal setup and broad shared-hosting compatibility.