Messaging between objects

chadjohnson

Suppose we're using an object-oriented framework for our web site. We're obviously going to have a few common objects used throughout the framework, such as User and DB (or just a DB connection link). How would you go about making these objects available inside of the member functions of your classes? Would you encapsulate them some common object, like "Settings" or "Context"? Would you make these objects available inside member functions via "global $VARIABLE_NAME;"? Pass them individually or the Settings/Context object as a whole as a constructor parameter for every object in your framework?

Surely someone else has faced this problem before...

NogDog

For something like a database class, I like to use the singleton pattern. Then I can access it from any other object without those objects causing multiples instances of the database class.
Singleton Database class:

<?php
class Database
{
   private static $instance;

   private function __construct() 
   {
      // do stuff/call methods to set up db connection
   }

   public static function getInstance() 
   {
      if (!isset(self::$instance)) {
         $c = __CLASS__;
         self::$instance = new $c;
      }
      return self::$instance;
   }

   // Prevent users to clone the instance
   public function __clone()
   {
      trigger_error('Clone is not allowed.', E_USER_ERROR);
   }

   // various DB methods would follow here
}

Using it in another class:

require_once 'Database.class.php';

class myClass
{
   private $db;

   public function __construct()
   {
      $db = Database::getInstance();
   }

   public function someMethod()
   {
      $sql = "SELECT * FROM table";
      $result = $this->db->query($sql);
   }
}

chadjohnson

Awesome. This rocks. I had not considered static functions.

Building on your idea, someone suggested the Registry pattern.

NogDog

If you really want to get into it, check out PHP 5 Objects, Patterns and Practice by Matt Zandstra.

MakTheYak

Thanks NogDog, that's really useful and a concept I wouldn't have considered had I not seen it here!

Just a quick question... is the function of self and $this identical or are there subtle differences?

Cheers 🙂

MakTheYak

<snip>

Sorry, it told me that my message was not posted because it was less than 30s since my last post... looks like it was lying!!

NogDog

Basically, $this-> means "this object", while self:: means "this class". You need to use self:: when referring to static variables or methods. Otherwise you'll normally want to use $this->.