protected static function _setup_db($connection_name = self::DEFAULT_CONNECTION)
{
if (!array_key_exists($connection_name, self::$_db) || !is_object(self::$_db[$connection_name])) {
self::_setup_db_config($connection_name);
$db = new PDO(self::$_config[$connection_name]['connection_string'], self::$_config[$connection_name]['username'], self::$_config[$connection_name]['password'], self::$_config[$connection_name]['driver_options']);
$db->setAttribute(PDO::ATTR_ERRMODE, self::$_config[$connection_name]['error_mode']);
self::set_db($db, $connection_name);
}
}