CreativeController.php

<?php

[...]

        // process form
        if ('POST' == $this->request->getMethod()) {
            // bind form data
            $form->bindRequest($this->request);

            // If form is valid
            if ($form->isValid() && ($creative = $form->getData()) instanceOf Creative) {
                $this->entityManager->persist($creative);
                $this->entityManager->flush();

                $this->get('session')->setFlash('notice', 'Successfully added creative to <strong>' . $offer->getName() . '</strong>!');
                return $this->redirect($this->generateUrl('offer_creative', array('id' => $offer->getId())));
            }
        }

[...]

CreativeFormType.php

<?php

[...]

    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
            ->add('name')
            ->add('description')
            ->add('html', 'textarea')
            ->add('active');
    }

[...]