CodeIgniter 4 Exam Cheat Sheet

1. What the exam task means

The task usually means: create or open a CodeIgniter 4 project, connect it to a MySQL database, fetch records from a table, and display them in a page.

Main flow: Browser → Route → Controller → Model → Database → View → Web page

Most important concepts

Route
Defines which URL calls which controller method.

Controller
Controls the logic and sends data to the view.

Model
Represents a database table.

View
HTML page that displays the data.

2. CodeIgniter 4 file structure you need

app/
├── Config/
│   └── Routes.php
├── Controllers/
│   └── Students.php
├── Models/
│   └── StudentModel.php
└── Views/
    └── students.php

.env
database.sql

Important: CodeIgniter 4 is not the same as CodeIgniter 3. Avoid exam examples using CI_Controller, CI_Model, or $this->load.

3. Database SQL example

Create a database and table. Example table: students.

CREATE DATABASE school;

USE school;

CREATE TABLE students (
  id INT AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(100) NOT NULL,
  email VARCHAR(100) NOT NULL
);

INSERT INTO students (name, email)
VALUES
('Ana', 'ana@test.com'),
('Marko', 'marko@test.com'),
('Sara', 'sara@test.com');

4. Database connection in .env

In CodeIgniter 4, database settings are usually placed in the .env file.

CI_ENVIRONMENT = development

database.default.hostname = localhost
database.default.database = school
database.default.username = root
database.default.password =
database.default.DBDriver = MySQLi
database.default.port = 3306

If the database does not connect, check database name, username, password, and whether MySQL is running.

5. Route pattern

File: app/Config/Routes.php

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

Part	Meaning
`/students`	The URL path in the browser.
`Students`	The controller class.
`index`	The method/function inside the controller.

6. Model pattern

File: app/Models/StudentModel.php

<?php

namespace App\Models;

use CodeIgniter\Model;

class StudentModel extends Model
{
    protected $table = 'students';
    protected $primaryKey = 'id';
    protected $allowedFields = ['name', 'email'];
}

Important model methods

Method	Use
`findAll()`	Gets all rows.
`find($id)`	Gets one row by ID.
`insert($data)`	Adds a new row.
`update($id, $data)`	Updates a row.
`delete($id)`	Deletes a row.

7. Controller pattern

File: app/Controllers/Students.php

<?php

namespace App\Controllers;

use App\Models\StudentModel;

class Students extends BaseController
{
    public function index()
    {
        $model = new StudentModel();

        $data = [
            'students' => $model->findAll()
        ];

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

What this does

use App\Models\StudentModel; imports the model.
$model = new StudentModel(); creates the model object.
$model->findAll() gets all students from the database.
return view('students', $data); opens the view and sends data to it.

8. View pattern

File: app/Views/students.php

<!DOCTYPE html>
<html>
<head>
    <title>Students</title>
</head>
<body>

<h1>Students</h1>

<?php foreach ($students as $student): ?>
    <p>
        <?= esc($student['name']) ?>
        -
        <?= esc($student['email']) ?>
    </p>
<?php endforeach; ?>

</body>
</html>

Use esc() when printing user/database data. It helps prevent unsafe HTML output.

9. Full minimal pattern to memorize

Route

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

Model

class StudentModel extends Model
{
    protected $table = 'students';
    protected $primaryKey = 'id';
    protected $allowedFields = ['name', 'email'];
}

Controller

$model = new StudentModel();

return view('students', [
    'students' => $model->findAll()
]);

View

<?php foreach ($students as $student): ?>
    <p><?= esc($student['name']) ?></p>
<?php endforeach; ?>

10. Extra CRUD examples

Insert data

$model->insert([
    'name' => 'Luka',
    'email' => 'luka@test.com'
]);

Find one row

$student = $model->find(1);

Update row

$model->update(1, [
    'name' => 'Updated Name'
]);

Delete row

$model->delete(1);

11. PHP operators you will see

Operator	Meaning	Example
`->`	Access object method/property	`$model->findAll()`
`=>`	Array key/value	`'students' => $students`
`::`	Static/class method reference	`Students::index`

12. Common errors and fixes

Error	Likely cause	Fix
404 page not found	Wrong route or controller name	Check `Routes.php` and controller class name.
Class not found	Wrong namespace or filename	Check `namespace App\Models;` and `use App\Models\StudentModel;`.
Database connection failed	Wrong `.env` details	Check database name, username, password, and MySQL server.
Undefined variable: students	Controller did not send data to view	Use `return view('students', ['students' => ...]);`.
No data displayed	Empty table or wrong table name	Check SQL data and `protected $table`.

13. Exam checklist

☐ MySQL is running

☐ Database exists

☐ Table has data

☐ .env database settings are correct

☐ Route points to controller

☐ Controller imports model

☐ Model has correct table name

☐ View uses correct variable name

14. Good Google searches during exam

CodeIgniter 4 model findAll example
CodeIgniter 4 database .env MySQLi
CodeIgniter 4 routes controller method
CodeIgniter 4 pass data to view
CodeIgniter 4 foreach view example
CodeIgniter 4 esc output

Avoid broad searches like CodeIgniter database tutorial, because many results may be CodeIgniter 3.