IndexController.php

/**
 * Retorna os comentários de um post
 * @return Zend\Http\Response 
 */
public function commentsAction()
{
    $id = (int) $this->params()->fromRoute('id', 0);
    $where = array('post_id' => $id);
    $comments = $this->getTable('Application\Model\Comment')
                     ->fetchAll(null, $where)
                     ->toArray();

    $response = $this->getResponse();
    $response->setStatusCode(200);
    $response->setContent(json_encode($comments));
    $response->getHeaders()->addHeaderLine('Content-Type', 'application/json');
    return $response;
}