CodeIgniter Application Architecture


📝 CodeIgniter Application Architecture

🔎 Introduction

CodeIgniter is built on the MVC (Model-View-Controller) architecture, which separates application logic from presentation. This design pattern ensures clean, maintainable, and scalable code.

Understanding the CodeIgniter application architecture is crucial for efficient development.

🏗️ 1. MVC Design Pattern

🔹 Model

  • Handles data and business logic.

  • Interacts with the database.

  • Example: Fetching users from a users table.

🔹 View

  • Handles presentation logic.

  • Displays data sent by the Controller in HTML/CSS format.

🔹 Controller

  • Acts as a bridge between Model and View.

  • Receives HTTP requests, processes input, interacts with Models, and loads Views.

📂 2. CodeIgniter Folder Structure and Role

Folder Purpose
app/ Contains application-specific code: Controllers, Models, Views, Config, Filters, etc.
system/ Contains core CodeIgniter framework files. Do not modify.
public/ Entry point (index.php) and public assets (CSS, JS, images).
writable/ Stores cache, logs, session data, and uploaded files.
vendor/ Third-party dependencies (Composer packages).
.env Environment-specific configurations.

🔄 3. Request Flow in CodeIgniter

Here’s how a request moves through the system:

  1. User Request:
    Browser requests a URL like /products/view/5.

  2. Front Controller (index.php):

    • Initializes CodeIgniter environment.

    • Loads required libraries and configurations.

  3. Routing:

    • Router identifies the Controller and method to execute based on URL and routes.php.

  4. Controller Execution:

    • Controller processes the request, validates input, and interacts with Models.

  5. Model Interaction:

    • Retrieves or updates data in the database.

  6. View Rendering:

    • Controller passes data to the View.

    • View generates HTML to display to the user.

  7. Response Sent:

    • Browser displays the final output.

📊 4. Layered Architecture Benefits

  • Separation of Concerns: Models handle data, Views handle presentation, Controllers handle logic.

  • Maintainability: Changes in one layer rarely affect others.

  • Reusability: Models and Views can be reused across different Controllers.

  • Testability: MVC makes unit testing easier.

🖼️ 5. Visual Representation

Browser
   |
   v
Front Controller (index.php)
   |
   v
Router → Determines Controller & Method
   |
   v
Controller → Processes Request
   |
   +--> Model → Fetches/Updates Data
   |
   +--> View → Generates HTML
   |
   v
Response Sent to Browser

🎯 Conclusion

The CodeIgniter application architecture revolves around MVC, ensuring clean separation between logic, data, and presentation. By understanding this architecture:

  • You can efficiently structure your applications.

  • Easily scale or maintain code.

  • Quickly onboard new developers to the project.