PHP Class Scope issues - php

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.