Nefunguje joinovanie tabuliek v Nette\Database

mam mysql databazu v nej dve tabulky:

CREATE TABLE  `nav` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(75) COLLATE utf8_slovak_ci NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_slovak_ci;

CREATE TABLE  `nav_item` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `nav_id` int(10) unsigned NOT NULL,
  `pos` int(10) unsigned NOT NULL,
  `name` varchar(75) COLLATE utf8_slovak_ci NOT NULL,
  `uri` varchar(75) COLLATE utf8_slovak_ci NOT NULL,
  `active` tinyint(1) unsigned NOT NULL DEFAULT '1',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_slovak_ci;

a v nette tento kod:

foreach ($db->table('nav_item')->where('nav.id = ?', 1) as $navItem)
	dump($navItem->name);

hadze mi to chybu „No reference found for $nav_item->nav.“

viete mi povedat kde ja chyba?