<?php
    public function getPrice($tracks = FALSE) {
        $price = 0;
        if(!$tracks) {
            $tracks = Doctrine_Query::create()->from('Song s')->where('s._album = ?', $this['_id'])->execute();
        }
        foreach($tracks as $track) {
            $price += $track->get_price();
        }
        return sprintf('%.2f', $price);
    }