function productCategoriesString()
    {
        $categories = $this->attribute( 'product_categories' );
        if ( !$categories )
        {
            $result = ezpI18n::tr( 'kernel/shop', 'Any' );
            return $result;
        }

        $categoriesNames = array();
        foreach ( $categories as $cat )
            $categoriesNames[] = $cat['name'];

        return join( ', ', $categoriesNames );
    }