CodeIgniter Framework: A Guide to Rapid PHP Web Application Development

This guide explores CodeIgniter, a lightweight and efficient open-source PHP framework. Learn about its key features, MVC architecture, and understand its simple structure for rapid web application development. The directory structure and its role in maintaining organized code are also explained.

CodeIgniter Interview Questions and Answers

What is CodeIgniter?

Question 1: What is CodeIgniter?

CodeIgniter is a free, open-source PHP framework for building dynamic websites. It's lightweight, uses the Model-View-Controller (MVC) design pattern, and offers a simple structure to create web applications quickly and efficiently.

Prominent Features of CodeIgniter

Question 2: Prominent Features of CodeIgniter

Key features:

Open-source and free.
Lightweight and fast.
Uses the MVC design pattern.
Robust database support.
Extensible using libraries and helpers.
Excellent documentation.

CodeIgniter Folder Structure

Question 3: CodeIgniter Folder Structure

The CodeIgniter directory structure provides organization and maintainability.

(A visual representation of the folder structure would be useful here, but can't be directly created in HTML. The description should list the major folders: application, system, etc., briefly explaining their purpose.)

CodeIgniter Architecture

Question 4: CodeIgniter Architecture

CodeIgniter's architecture is dynamically instantiated (lightweight), loosely coupled (components have minimal dependencies), and uses components with well-defined responsibilities. This improves flexibility and maintainability.

(A diagram illustrating the data flow within the MVC architecture would be helpful but is not directly representable in HTML.)

MVC in CodeIgniter

Question 5: MVC in CodeIgniter

CodeIgniter uses the MVC (Model-View-Controller) pattern:

Model: Manages data (database interaction).
View: Displays data to the user (HTML templates).
Controller: Handles user requests and interacts with the model and view.

Models in CodeIgniter

Question 6: Models in CodeIgniter

Models handle data logic and database interactions. They're located in the application/models directory.

Example Model Structure


<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class MyModel extends CI_Model {
    // ... your model methods ...
}
?>

Loading Models

Question 7: Loading Models in CodeIgniter

To load a model in a controller:

PHP Code


$this->load->model('MyModel');

Manual Database Connection

Question 8: Manual Database Connection

To manually connect to a database:

PHP Code


$this->load->database();

Views in CodeIgniter

Question 9: Views in CodeIgniter

Views contain the presentation logic (HTML templates). They're located in the application/views directory and are loaded by controllers.

Example View


<?php
defined('BASEPATH') OR exit('No direct script access allowed');
?>
<html>
<body>
  <p>This is a view.</p>
</body>
</html>

Loading Views

Question 10: Loading Views in CodeIgniter

To load a view in a controller:

PHP Code


$this->load->view('my_view');

Controllers in CodeIgniter

Question 11: Controllers in CodeIgniter

Controllers handle user requests, interact with models, and load views. They are the central point of request handling.

Example Controller Structure


<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Main extends CI_Controller {
    public function index() {
        // ... your controller logic ...
    }
}
?>

Default Controller

Question 12: Default Controller

The default controller in CodeIgniter is specified in application/config/routes.php. It's the controller that's loaded when no controller is specified in the URL.

Setting Default Controller


$route['default_controller'] = 'Welcome'; // Example

Calling Constructors

Question 13: Calling Constructors

To call the parent class constructor in CodeIgniter, use parent::__construct(); within your class's constructor.

CodeIgniter URL Structure

Question 14: CodeIgniter URL Structure

CodeIgniter uses a segment-based URL structure:

example.com/controller/method/id

Error Handling (Inhibitors)

Question 15: Inhibitors

Inhibitors are CodeIgniter's error handlers. They manage various types of errors (exceptions, parse errors, fatal errors) and provide ways to handle these errors gracefully.

Default Controller Method

Question 16: Default Method Name

The default method in a CodeIgniter controller is index(). If you don't specify a method in the URL, the index() method will be called.

Remapping Method Calls

Question 17: Remapping Method Calls

The _remap() method in CodeIgniter allows you to redirect or handle URI requests that would normally call different methods.

Example _remap() Method


public function _remap($method) {
    if (method_exists($this, $method)) {
        $this->$method();
    } else {
        show_404(); // Or handle the case where the method doesn't exist
    }
}

Helpers

Question 18: Helpers in CodeIgniter

Helpers are collections of functions that provide commonly needed functionality (e.g., URL helpers, form helpers, text helpers).

Loading Helpers


$this->load->helper('url'); //Loads the URL helper

Loading Multiple Helpers

Question 19: Loading Multiple Helpers

Load multiple helpers by specifying them in an array:

PHP Code


$this->load->helper(array('url', 'form', 'text'));

Libraries

Question 20: Libraries in CodeIgniter

Libraries extend CodeIgniter's functionality. They are loaded using $this->load->library('library_name');.

Creating Libraries

Question 21: Creating Libraries

You can create new libraries, extend existing ones, or replace them in CodeIgniter.

Question 22: Library Storage Location

New libraries are typically placed in the application/libraries directory.

Extending Native Libraries

Question 23: Extending Native Libraries in CodeIgniter

You can extend CodeIgniter's built-in libraries by creating a new class that inherits from the original library class. This is preferable to replacing the entire library, as it allows you to add functionality without affecting the original library's behavior.

To create an extended library:

Create a new file named MY_<LibraryName>.php in the application/libraries folder.
The class name should be MY_<LibraryName> and extend the original library class (e.g., CI_<LibraryName>).

Example: Extending CI_Calendar


<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class MY_Calendar extends CI_Calendar {
    // Add your custom methods here
}
?>

Extending Classes

Question 24: Extending Classes in CodeIgniter

You can extend a class (including CodeIgniter's core classes) by creating a file in the application/core directory and defining a class that extends the original class. This allows you to add methods or modify the behavior.

Example: Extending CI_Input


<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class MY_Input extends CI_Input {
    // Add your custom methods here
}
?>

Routing in CodeIgniter

Question 25: Routing in CodeIgniter

CodeIgniter's routing allows you to define custom URLs to improve SEO and simplify navigation. You use wildcards and regular expressions to define rules that map URLs to controllers and methods.

Example Route (Wildcard)


$route['products/:num'] = 'products/view/$1'; // :num matches a number

Example Route (Regular Expression)


$route['blog/([a-z0-9]+)'] = 'blog/view/$1'; // Matches alphanumeric characters

Reasons for Configuring URL Routes

Question 26: Why Configure URL Routes?

Reasons to configure routes include improving SEO, hiding complex code structures from URLs, and creating more user-friendly URLs.

Hooks in CodeIgniter

Question 27: Hooks in CodeIgniter

Hooks provide a way to modify CodeIgniter's behavior without modifying core files. You define hook points and the functions to execute at those points in application/config/hooks.php.

Enabling Hooks

Question 28: Enabling Hooks in CodeIgniter

To enable hooks, set $config['enable_hooks'] = TRUE; in application/config/config.php.

Hook Points

Question 29: Hook Points in CodeIgniter

CodeIgniter offers various hook points:

pre_controller
post_controller_constructor
pre_system
post_system
cache_override
display_override
post_controller

Drivers in CodeIgniter

Question 30: Drivers in CodeIgniter

Drivers are a specialized type of library in CodeIgniter. They are often used for database connections and other situations where different implementations are needed. They have a parent class and extendable child classes that inherit from the parent but not each other.

Initializing Drivers

Question 31: Initializing Drivers

Initialize a driver using:

PHP Code


$this->load->driver('database'); // Example

Creating Drivers

Question 32: Creating Drivers

Creating a driver involves defining the driver's structure, adding it to the driver list, and implementing the driver classes.

Multiple Database Connections

Question 33: Connecting Multiple Databases

Connect to multiple databases using the database config array and specifying the database group name:

PHP Code


$db1 = $this->load->database('group_one', TRUE);
$db2 = $this->load->database('group_two', TRUE);

Printing SQL Statements

Question 34: Printing SQL Statements

(This requires more context. Methods for printing or logging SQL queries within a CodeIgniter model would depend on the database library used and logging mechanisms implemented.)

CodeIgniter Security Methods

Question 35: CodeIgniter Security Methods

CodeIgniter provides security features such as XSS (Cross-Site Scripting) filtering and CSRF (Cross-Site Request Forgery) protection.

XSS Filtering

Question 36: XSS Security Parameters

CodeIgniter uses the xss_clean() method for XSS filtering. It converts potentially malicious characters into HTML entities.

PHP Code


$safe_data = $this->security->xss_clean($data);

CSRF Protection

Question 37: Preventing CSRF Attacks

CodeIgniter's CSRF (Cross-Site Request Forgery) protection uses a hidden token to verify that a request originates from your website. This token is usually generated with each request.

Enabling CSRF Protection

Question 38: Enabling CSRF Protection

Enable CSRF protection by setting $config['csrf_protection'] = TRUE; in application/config/config.php.

CSRF Attacks

Question 39: CSRF Attacks

CSRF attacks trick a user's browser into sending unwanted requests to a website. CodeIgniter's CSRF protection helps mitigate this risk by verifying that the request comes from your website.