PHP Class Scope issues

Question

Below is a very basic example of the trouble I am having.

Now why must I use $session = new Session(); in the database.class.php file when in my system the files are included in a way that it would be visible already.

In other words I cannot call $session = new Session(); outside of any other classes, to make it work in other classes I have to call create a new objectof the session class in every class I want to use it in, how can I avoid this and make it work without doing that?

// Session.class.php
class Session{

    public function __construct()
    {
     session_start();
    }

    public function set($name, $value)
    {
     $_SESSION[$name] = $value;
    }
}

...

// Database.class.php
class Database{

    public static function mysql_query_2($query)
    {
     if ($session->get('user_role') == 10){
      $_SESSION['queries']++;
     }
     return mysql_query($query);
    }
}

Answer 1

First and foremost, your Session class should be a singleton - the reason is that multiple calls to session_start() will get you nothing but problems (session id gets regenerated)

So...

/**
 * Session singleton class
 */
class Session
{
    // prevents object instanciation ($obj = new Session())
    protected function __construct() {
        session_start();
    }

    // prevents object cloning
    protected function __clone() {}

    public static function getInstance()
    {
     static $instance = null;
     if ($instance == null)
      $instance = new Session();
     return $instance;
    }

    // rest of the code
}

To use it you simply call:

$sess = Session::getInstance();
$sess->doSomething();

or simply

Session::getInstance()->doSomething();

Anywhere you need to use the session class.

Update: - I see you probably don't grasp the concept of singletons yet, so here's a proper wikipedia link 8)

Answer 2

If I understand your problem correctly, one solution to your problem is to use a Singleton.

final class Singleton {

    protected static $_instance;

    // Singleton can't be constructed or cloned
    protected function __construct(){ }  
    protected function __clone() { }

    // Create an instance if necessary and return an instance.
    public static function getInstance(){
      if( self::$_instance === NULL ) {
        session_start();
        self::$_instance = new self();
      }
      return self::$_instance;
    }

    public function set($name, $value){
        $_SESSION[$name] = $value;
    }
}

In index.php you would have:

$session = Session::getInstance();
$session->get();

Then in your Database class you would have:

// Database.class.php
class Database{

    public static function mysql_query_2($query)
    {
        if (Session::getInstance()->get('user_role') == 10){
                $_SESSION['queries']++;
        }
        return mysql_query($query);
    }
}

You would only ever create one instance of the Session class (which is what I think your looking for). Then when you need the Session class somewhere else (ie your Database class) you just call Session::getInstance() again. There is only one instance of Session ever created and you can use it globally across your script.