$hasProductTag = false;
foreach ($Product->getProductTag as $ProductTag) {
    if (!is_null($ProductTag) && $ProductTag->getTag()->getId() == 3) {
        $hasProductTag = true;
        break;
    }
}

return $app->render('Product/detail.twig', array(
    'title' => $this->title,
    'subtitle' => $Product->getName(),
    'form' => $form->createView(),
    'Product' => $Product,
    'is_favorite' => $is_favorite,
    'hasProductTag ' => $hasProductTag,
));