Unit 03

MVC stands for Model–View–Controller. It is a software design pattern used in CodeIgniter to divide an application into three separate components, with each component having a specific responsibility.

MVC separates business logic, presentation, and user requests, making the application easier to develop, understand, maintain, and modify.

MVC Architecture

User / Browser
                    |
                    | HTTP Request
                    ↓
              ┌─────────────┐
              │ Controller  │
              └─────────────┘
                /         \
               /           \
              ↓             ↓
       ┌─────────────┐  ┌─────────────┐
       │    Model    │  │    View     │
       └─────────────┘  └─────────────┘
              |               |
              ↓               ↓
          Database        Web Page/UI

class StudentModel extends Model
{
    public function getStudents()
    {
        return $this->findAll();
    }
}

<h2>Student Details</h2>

<p>Name: Rahul</p>
<p>Course: BCA</p>

class Student extends BaseController
{
    public function index()
    {
        $model = new StudentModel();
        $data['students'] = $model->getStudents();

        return view('students', $data);
    }
}

Working of MVC

User Request → Controller → Model → Database

Model → Controller → View → Response to User

For example, when a user requests a student page:

Step 1: The Controller receives the request.

Step 2: The Controller asks the Model for student data.

Step 3: The Model retrieves the data from the database.

Step 4: The Model returns the data to the Controller.

Step 5: The Controller passes the data to the View.

Step 6: The View displays the student information to the user.

Advantages of MVC

URL Routing is the process of connecting a URL requested by the user to a specific controller and its method in a CodeIgniter application.

URL → Route → Controller → Method → Response

For example, when the user visits http://localhost/myproject/course, CodeIgniter checks the defined routes and determines which controller method should execute: /course → Course Controller → index().

What is a Route?

A route defines which controller method should be executed when a particular URL is requested. In CodeIgniter 4, routes are generally defined in app/Config/Routes.php.

$routes->get('/course', 'Course::index');

This means /course is the URL, Course is the Controller, index is the Controller method, and get() represents an HTTP GET request.

Types of Routing in CodeIgniter 4

$routes->get('/course', 'Course::index');

/course/index
      ↓
Course::index()

Example of Routes.php

<?php

use CodeIgniter\Router\RouteCollection;

$routes->get('/', 'Home::index');
$routes->get('course', 'Course::index');
$routes->post('course/save', 'Course::save');

For example, $routes->post('course/save', 'Course::save'); means that when a form sends data to /course/save using POST, CodeIgniter executes the save() method of the Course controller.

Default Controller and Default Route

The default controller is the controller loaded when the user visits the application's base URL without specifying a controller. For example, http://localhost/myproject/ can execute Home::index().

The default route is normally defined in app/Config/Routes.php:

$routes->get('/', 'Home::index');

Here / represents the root URL, Home is the controller, and index is the method.

PHP provides two main extensions for connecting with MySQL databases: MySQLi (MySQL Improved) and PDO (PHP Data Objects). Both can be used to connect PHP applications with databases and support prepared statements, which help protect applications from SQL injection.

<?php

$host = "localhost";
$user = "root";
$password = "";
$database = "ComplaintDB";

$conn = new mysqli($host, $user, $password, $database);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

echo "Database connected successfully";
?>

<?php

$host = "localhost";
$db = "ComplaintDB";
$user = "root";
$password = "";

$conn = new PDO(
    "mysql:host=$host;dbname=$db",
    $user,
    $password
);

$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

echo "Database connected successfully";
?>

MySQLi vs PDO

Database Connection in CodeIgniter

CodeIgniter provides a database layer so that the Model can connect to the database and perform operations such as findAll() (retrieve all records), find() (retrieve a record), insert() (insert data), update() (update data), and delete() (delete data). For example:

<?php

namespace App\Models;

use CodeIgniter\Model;

class CourseModel extends Model
{
    protected $table = 'course';
    protected $primaryKey = 'Id';
    protected $allowedFields = ['Id', 'Name'];
    protected $returnType = 'array';
}

The CodeIgniter Model provides these built-in database functions and works with the specified course table.

Working

Controller
     ↓
Model
     ↓
Database
     ↓
Model
     ↓
Controller
     ↓
View

For example, the Controller can create a CourseModel object and use:

$model = new CourseModel();
$data['courses'] = $model->findAll();

return view('course_form', $data);

Here, findAll() retrieves the course records from the database and the Controller sends them to the View.

Session in CodeIgniter is used to store user data across multiple requests. It can be used for information such as user ID, username, and login status.

Flashdata is a special type of session data that is stored temporarily and is automatically removed after it is used. It is commonly used for success and error messages.

session()->set([
    'username' => 'Rahul',
    'user_id' => 101
]);

$username = session()->get('username');

session()->remove('username');

session()->setFlashdata(
    'message',
    'Registration successful!'
);

$message = session()->getFlashdata('message');

Difference Between Session and Flashdata

Example

// Store user information
session()->set('username', 'Rahul');

// Retrieve user information
$username = session()->get('username');

// Store temporary success message
session()->setFlashdata(
    'message',
    'Data saved successfully!'
);

// Retrieve temporary message
$message = session()->getFlashdata('message');

File management in CodeIgniter refers to handling files uploaded by users, such as images, documents, and other files. CodeIgniter provides the $this->request object and an UploadedFile object to obtain and manage uploaded files.

A common approach is to create an upload folder inside the project's public directory, for example public/Uploads/.

Steps for File Upload

public/Uploads/

Example:
C:\xampp\htdocs\codeigniter4-framework\public\Uploads

$file = $this->request->getFile('myfile');

if ($file->isValid()) {
    // File is valid
}

$newName = $file->getRandomName();

$file->move('public/Uploads', $newName);

Complete Example

HTML Form

<form action="/upload" method="post" enctype="multipart/form-data">

    <input type="file" name="myfile">

    <button type="submit">Upload</button>

</form>

Controller

public function upload()
{
    $file = $this->request->getFile('myfile');

    if ($file->isValid()) {

        $newName = $file->getRandomName();

        $file->move('public/Uploads', $newName);

        return "File uploaded successfully";
    }

    return "File upload failed";
}

Important File Management Methods

CodeIgniter provides Helpers and Libraries to simplify common web-development tasks. They provide reusable functionality so that developers do not have to write the same code repeatedly.

helper('url');

$validation = \Config\Services::validation();

$validation->setRules([
    'name'  => 'required',
    'email' => 'required|valid_email'
]);

Difference Between Helpers and Libraries

Advantages