OOP - sql commands inside PHP class - php

Question

I have a website written with procedural PHP and now I'm re-coding it in (at least partly) OOP style so that I can start learning it. It is a simple page displaying several learning courses (title, description, etc) from a database. The admin can add or delete anything so it has to be dynamic.
At first I ran a single line of code:
$courses=$pdo->run("SELECT id,title,description FROM courses WHERE status=1 ORDER BY id")->fetchAll(PDO::FETCH_CLASS, 'Course');
$cmax = count($courses);
and echoed e.g. $courses[3]->description but I felt like I'm doing nothing else but pretending OOP while just using a multidimensional array. Again, it would be ok for the purpose of the website but my question is, in order to get used to OOP logic, can I do it like this: I'm generating a dropdown menu with only the titles and IDs from the database, and after either is clicked, only then I'm creating the object (to get the description, date, teacher, whatever):
$obj = new Course($pdo,$userSelectedID);
echo $obj->getTitle($pdo);
$obj->showDetails($pdo); // etc
The class:
class Course {
protected $id;
protected $title;
protected $description;
public function __construct($pdo,$id) {
$this->id=$id;
}
public function getTitle($pdo) {
$this->title=$pdo->run("SELECT title FROM courses WHERE id=?",[$this->id])->fetchColumn();
return $this->title;
}
public function getDescription($pdo) {
$this->description=$pdo->run("SELECT description FROM courses WHERE id=?",[$this->id])->fetchColumn();
return $this->description;
}
public function showDetails($pdo) {
echo "<h3>".$this->getTitle($pdo)."</h3>".$this->getDescription($pdo);
}
}
Is this a wrong approach? Is it ok to run sql commands inside a class? Especially when I already had to use some DB data to generate the dropdown menu. I hope my question makes sense.
PS: I've heard passing the PDO object every time isn't the best practice but I'm not there yet to do it with the recommended instance(?)

Answer 1

A good approach is to create model classes for every table you have in your database.
A model contains private attributes corresponding yo your table columns, with associated getters and setters.
For your Course table:
class Course {
protected $id;
protected $title;
protected $description;
public function getId() {
return $this->id;
}
public function setId($id) {
$this->id = $id;
}
public function getTitle() {
return $this->title;
}
public function setTitle($title) {
$this->title = $title;
}
public function getDescription() {
return $this->description;
}
public function setDescription($description) {
$this->description = $description;
}
}
Then, you have the concept of Data Access Objects. You can create an abstract class that will be extended by your data access objects:
abstract class AbstractDAO {
protected $pdo;
public function __construct($pdo)
{
$this->pdo = $pdo;
}
abstract public function find($id);
abstract public function findAll();
abstract protected function buildModel($attributes);
}
For your course table:
class CourseDAO extends AbstractDAO {
public function find($id) {
$statement = $this->pdo->prepare("SELECT * FROM courses WHERE id = :id");
$statement->execute(array(':id' => $id));
$result = $statement->fetch(PDO::FETCH_ASSOC);
return $this->buildModel($result);
}
public function findAll() {
$statement = $this->pdo->prepare("SELECT * FROM courses");
$statement->execute();
$results = $statement->fetchAll(PDO::FETCH_ASSOC);
$courses = [];
foreach($results as $row)
$courses[] = $this->buildModel($row);
return $courses;
}
public function findByTitle($title)
{
...
}
public function create(Course $course)
{
...
}
protected function buildModel($attributes) {
$course = new Course();
$course->setId($attributes['id']);
$course->setTitle($attributes['title']);
$course->setDescription($attributes['description']);
return $course;
}
}
Modern frameworks do this automatically, but I think it is good to understand how it works before using powerful tools like Eloquent or Doctrine