my-plugin-post-meta-class.php

<?php 

/**
 * Class that manages all post meta attached to posts by my plugin. This class can be used as an
 * ordinary PHP object (stdClass)
 * 
 * @requires PHP version >= 5.1, WordPress version >= 1.6
 * @package MyPlugin
 * @since 0.1
 */
class MyPlugin_Post_Meta implements IteratorAggregate {

  public static function get($name, $default=false, $ns = null) 
  {
    $obj = new self($ns);
    $val = $obj->$name;
    if($val === false && $default !== false) 
      $val = $default;
    return $val;
  }

  public static function set($name, $val, $ns=null) 
  {
    $obj = new self($ns);
    $obj->$name = $val;
  }
  
  private $ns;
  private $post_id;

  public function __construct($post_id=null, $ns = null) 
  {
    if($post_id === null) {
      global $post;
      $this->post_id = $post->ID;
    } else {
      $this->post_id = $post_id;      
    }
    if( $ns === null )
      $ns = plugin_basename(__FILE__);
      
    $this->ns = '_'.$ns.'_';
  }

  public function __get($name) 
  {
    return get_post_meta($this->post_id, $this->ns . $name, true);
  }

  public function __set($name, $val) 
  {
    if($val === null) {
      $this->delete($name);
    } else {
      update_post_meta($this->post_id, $this->ns . $name, $val);
    }
  }
  
  public function __isset($name)
  {
    return $this->exists($name);
  }

  public function __unset($name)
  {
    $this->delete($name);
  }

  public function exists($name) {
    return $this->$name ? true:false;
  }

  public function deleteAll() {
    global $wpdb;
    $wpdb->query("
        DELETE `meta_key`, `meta_value`
        FROM $wpdb->postmeta
        WHERE 
          `post_id` = $post_id 
          AND `meta_key` LIKE '".$this->ns."%'
    ");
    clean_post_cache( $this->post_id );    
  }

  public function delete($name) {
    delete_post_meta($this->post_id, $this->ns . $name);
  }
  
  public function getIterator() 
  {
    global $wpdb;
    $data = array();
    $wpdb->query("
        SELECT `meta_key`, `meta_value`
        FROM $wpdb->postmeta
        WHERE `post_id` = $post_id
    ");
    $ns_length = strlen($this->ns);
    foreach($wpdb->last_result as $k => $v) {
      if( substr($k->meta_key, 0, $ns_length) == $this->ns )
        $data[$v->meta_key] =   $v->meta_value;
    }
    return new ArrayIterator($data);
  }

}


// Use this class as an ordinary php object (stdClass)

$meta = new MyPlugin_Post_Meta();

$meta->some_option = 'My value'; // the value can be of any type

if( isset($meta->other_option) ) { 
  unset( $meta->other_option );
}

if( $meta->perhaps_a_meta ) { // trying to access undefined meta will return false (no error triggered)
  //...
}

foreach( $meta as $meta_name => $val) { // tou can traverse the option object as if it were an array
  // ...
}


// Static short hand functions (post needs to be in global)
MyPlugin_Post_Meta::get('some_option', 'default value');  
MyPlugin_Post_Meta::set('some_option', null); // setting the meta to null will remove it