gistfile1.php

<?php

class activity_box {

  private $items = array();
  private $user_id;
  private $exists = true;

  public function __construct($user_id) {
    $this->user_id = (int) $user_id;

    $result = registry::$db->query('SELECT object FROM activity_box WHERE user_id = ' . $this->user_id;
    $this->items = unserialize(registry::$db->fetch_field('object', $result);

    if (!$this->items) {
      $this->items = array();
      $this->exists = false;
    }
  }

  public function add(activity_item $item) {
    $this->items[] = $item;
  }

  public function get_items() {
    // do some sorting of items first (usort)...
    return $items;
  }

  public function save() {
    if ($this->exists) {
      registry::$db->sql_query('UPDATE activity_box SET object = \'' . registry::$db->escape(serialize($this->items)) . '\' WHERE user_id = ' . $this->user_id;
    } else {
      registry::$db->sql_query('INSERT INTO activity_box (user_id, object) VALUES (' . $this->user_id . ', \'' . registry::$db->escape(serialize($this->items)) . '\'';
    }
  }

}