public function executeShow()
{
    $this->forward404Unless($this->hasRequestParameter('permalink') > 0);

    $pager   = new sfPropelPager('Product');
    $pager->init();
    $pager->setCursor($this->getRequestParameter('permalink'));
    $this->previous = $pager->getPrevious();
    $this->product  = $pager->getCurrent();
    $this->next     = $pager->getNext();
}