Learning OOP - distributing logic and dividing responsibility - php

Question

Trying to move from global procedural coding to a more OOP-oriented style, I'm refactoring a website for a magazine.
One of the conditions to check on the server is whether an article id or a combination of year/issue has been passed in. In the first case the user should be served a specific article, in the second case the table of contents and the image cover for the selected issue. I also need to retrieve the year and issue for display purposes in the second case.
My first instinct was to put all the the logic inside the constructor:
class Magazine {
public $year;
public $issue;
public function __construct($year, $issue, $articleId = 0) {
if($articleId > 0) {
// Get article from database
$this->year = // get year from search results;
$this->issue = // get number from search results;
} else {
// Get table of contents and cover image
}
}
}
// Create an instance either like this:
$magazine = new Magazine(1985, 3);
// Or like this:
$magazine = new Magazine(0, 0, 172);
But then I realized that it's probably not a good idea to "overload" the constructor in this way (to compensate for not being able to overload it in the usual sense?).
Ok, so I create a method for retrieving the article, like so:
class Magazine {
public $year;
public $issue;
private $articleId;
public function __construct($year, $issue, $articleId = 0) {
$this->year = $year;
$this->issue = $issue;
$this->articleId = $articleId;
}
public function getArticle() {
// Use $this->articleId to retrieve data from database
// Set $this->year and $this->issue to appropriate values
}
}
Or without a constructor:
class Magazine {
public $year;
public $issue;
public function getArticle($articleId) {
// Use $articleId to retrieve data from database
// Set $this->year and $this->issue to appropriate values
}
}
No, assigning values to the year and issue properties is not part of getting an article. So I create another method for that:
public function getYearAndIssue($articleId) {
// Use $articleId to retrieve data from database
}
But now I need to connect to the database twice. Not good. It seems like I have to collect all the data I need when connecting to the db the first time. And where do I do that? In the constructor? No, that will just take me back to square one. Or minus one.
So where do I go from here? Two methods like getArticleAndEverythingElseINeedForThat() { // ... } and getCoverAndEverythingElseINeedForThat() { ... }?
EDIT: Thanks to Daan’s comment I've experimented some more and come up with the following:
class Magazine {
private $db;
public function __construct($db) {
$this->db = $db;
}
public function getArticle($articleId) {
$sql = "SELECT article FROM table WHERE id = :id";
$ph = array(':id' => $articleId);
$ps = $this->db -> prepare($sql);
$ps -> execute($ph);
// Do some more stuff
return $article;
}
public function getYearAndIssue($articleId) {
$sql = "SELECT year, issue FROM table WHERE id = :id";
$ph = array(':id' => $articleId);
...
return array($year, $issue);
}
}
class Database {
public static function getConnection() {
$db = new PDO(...);
$db->setAttribute(...);
...
return $db;
}
}
$db = Database::getConnetion();
$magazine = new Magazine($db);
$article = $magazine->getArticle(59);
list($year, $issue) = $magazine->getYearAndIssue(59);
New questions:
Do I seem close to understand injection?
In some descriptions I've seen the PDO object is created both as a private variable in the constructor and passed as an argument to the helper functions, i.e. as if I'd written my code like this:
class Magazine {
private $db;
public function __construct($db) {
$this->db = $db;
}
public function getArticle($db, $articleId) {
// ...
}
}
$db = Database::getConnetion();
$magazine = new Magazine($db);
$article = $magazine->getArticle($db, 59);
Should I do that too? If so, why?
Even if I use the same db connection twice (or more times in the real scenario), I still have to get stuff from the db several times. Wouldn't it be better/faster to get everything I need from the db at once (if it would be possible without messing up the logic again/any further)? Like this:
$sql = "SELECT article, year, issue FROM table WHERE id = :id";