Question

I am new to OOP and I have recently asked question, which have thaught me that:

• every “operation” should be implemented in seperate class,
• issue I have faced should be resolved with dependency injection,
• I must not have one object for entire application.

Let’s say I have the following code:

class FtpConnect {
     public $server;

     private function connect () { ... }

     public __construct ($db, $mailer, $server) {
         $this->server = $server;
         $this->connect();
     } 
}

class Database {
    public $database_property;
    ...
}

class Phpmailer {
    public $phpmailer_property;
    ...
}

$db = new Database();
$mail = new Phpmailer();

$ftp = new Ftpconnect ($db, $mail, "ftp.mozilla.org");

$ftp->db->database_property;
$ftp->mail->phpmailer_property;

Is this a proper approach? It seems that I still have one object $ftp.

Reading property or calling methods like $ftp->db->database_property; is this the proper way?

Answer 1

There are a few good things and a few bad things in your example! First, congratulations for your serious attempt to learn good programing practices. You’re going the right direction!

Good things:

• you’re using proper constructor injection (form of DI) and therefore you are only writing new statements on the highest level of your example and none inside of classes.
• you have written a class for each of the different services, great.

Bad things:

• you’re accessing properties of db and mail through the ftp instance, don’t do that!
• you’re using public properties, make properties private and use public getters and setters
• you’re calling main methods in in the constructor, don’t do that, you should not call it inside the class but outside.
• you’re not doing anything with the $mailer instance passed to the ftp instance, does the ftp class really need the mailer class at all?

Improved example, assuming your ftp class really needs both database and mail:

class FtpConnect {

     private $db;
     private $mailer;

     private $server;

     public function connect () { ... }

     public __construct ($db, $mailer, $server) {
         $this->setServer($server);
         $this->setMailer($mailer);
         $this->setDb($db);
     }

     public setServer($server)
     {
         $this->server = $server;
     }

     public setDb($db)
     {
         $this->db = $db;
     }

     public setMailer($mailer)
     {
         $this->mailer = $mailer;
     }
}

class Database {
    private $databaseProperty;
    public getDatabaseProperty()
    {
        return $this->databaseProperty;
    }
}

class Phpmailer {
    private $phpmailerProperty;
    public ... see above...
}

$db = new Database();
$mail = new Phpmailer();

$ftp = new FtpConnect ($db, $mail, "ftp.mozilla.org");
$ftp->connect();

$someProperty = $db->getDatabaseProperty();