CodeIgniter Project Structure

Below is a clear explanation of the CodeIgniter project structure, focusing on CodeIgniter 4 (with a short note on CI3 at the end).

CodeIgniter 4 Project Structure

codeigniter4/
│
├── app/
├── public/
├── system/
├── writable/
├── env
├── spark
└── composer.json

1. app/ (Main Application Folder)

This is where you write most of your code.

app/
├── Config/
├── Controllers/
├── Models/
├── Views/
├── Database/
├── Filters/
├── Helpers/
├── Language/
└── Libraries/

???? Controllers/

Handles user requests and application flow.

class Home extends BaseController
{
    public function index()
    {
        return view('home');
    }
}

???? Models/

Manages database interactions.

class UserModel extends Model
{
    protected $table = 'users';
}

???? Views/

Contains UI files (HTML, CSS, JS).

<h1>Welcome to CodeIgniter</h1>

???? Config/

Application configuration files:

• App.php → baseURL, app name

• Database.php → database settings

• Routes.php → URL routing

???? Database/

Database-related files:

Database/
├── Migrations/
├── Seeds/
└── Factories/

• Migrations → version control for database schema

• Seeds → insert dummy data

???? Filters/

Middleware-like logic (auth, CSRF, etc.)

???? Helpers/

Reusable functions (form, URL, text helpers)

???? Language/

Multilingual support files

???? Libraries/

Custom libraries and classes

2. public/ (Web Root)

public/
├── index.php
├── .htaccess
└── assets/

• Entry point of the application

• CSS, JS, images go inside assets/

3. system/ (Core Framework)

• Contains CodeIgniter core files

• ❌ Do NOT modify

4. writable/ (Writable Directory)

writable/
├── cache/
├── logs/
├── session/
└── uploads/

• Cache

• Logs

• File uploads

• Must have write permissions

5. env / .env

Environment configuration:

CI_ENVIRONMENT = development

6. spark

Command-line tool for:

• Creating controllers/models

• Running migrations

• Starting server

Example:

php spark make:controller Home

7. composer.json

• Dependency management

• Autoloading

CodeIgniter 3 Structure (Quick Comparison)

application/
├── controllers/
├── models/
├── views/
├── config/
system/

Key Differences: CI3 vs CI4

Summary

• app/ → your application code

• public/ → web-accessible files

• system/ → framework core

• writable/ → cache, logs, uploads