在我的singleton中，我有以下函数

class plugin {

  private static $_instance;

  private function __construct() {
    //does all add_actions & filters
    $this->_register_hooks();
  }


  public static function getInstance() {
    if ( ! ( self::$_instance instanceof self ) ) {
        self::$_instance = new self();
    }

    return self::$_instance;
  }

  static function create_order_table() {
    global $wpdb;

      $table_name = $wpdb->prefix . "order";
      $charset_collate = $wpdb->get_charset_collate();

      $sql = "CREATE TABLE $table_name (
        id mediumint(9) NOT NULL AUTO_INCREMENT,
        name varchar(200) NOT NULL,
        description int(11) NOT NULL,
        alt_text int(11) NOT NULL,
        sort_order int(11) NOT NULL,
        time datetime DEFAULT \'0000-00-00 00:00:00\' NOT NULL,
        PRIMARY KEY  (id)
      ) $charset_collate;";

      require_once( ABSPATH . \'wp-admin/includes/upgrade.php\' );
      dbDelta( $sql );

      add_option( \'db_version\', DB_VERSION );
  }


 /**
  * ATIVATION
  * on activation the plugin creates databases
  * @access public
  * @since 1.0
  */
  public function activate() {

        // DATABASE
        //creates table
    register_activation_hook( __FILE__, array( &$this, \'create_order_table\' ) );
  }
}

global $plugin;

if ( ! $plugin ) {
  $plugin = plugin::getInstance();
  $plugin->activate();
}

非常感谢您的帮助。