Entities relation, form builder - symfony

Question

i have two entities Topic
and TopicContent
when i send data from Topic entity, all ok. But when i included TopicContentType to my form builder, a have an error.. Friends, help me please..
My controller
public function createAction(Request $request)
{
$entity = new Topic();
$form = $this->createCreateForm($entity);
$form->handleRequest($request);
if ($form->isValid()) {
$em = $this->getDoctrine()->getManager();
$em->persist($entity);
$em->flush();
return $this->redirect($this->generateUrl('application_club_show', array('id' => $entity->getTopicId())));
}
return $this->render('ApplicationClubBundle:Topic:new.html.twig', array(
'entity' => $entity,
'form' => $form->createView(),
));
}
$builder
->add('user_id', 'hidden')
->add('topic_title')
->add('topic_tags')
->add('topic_publish', 'hidden')
->add('topic_user_ip', 'hidden')
->add('topic_count_read', 'hidden')
->add('topic_count_comment', 'hidden')
;
$builder->add('topic_content', new \Application\ClubBundle\Form\TopicContentType());
TypicType
$builder
->add('user_id', 'hidden')
->add('topic_title')
->add('topic_tags')
->add('topic_publish', 'hidden')
->add('topic_user_ip', 'hidden')
->add('topic_count_read', 'hidden')
->add('topic_count_comment', 'hidden')
;
$builder->add('topic_content', new \Application\ClubBundle\Form\TopicContentType());
TopicContentType
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('topic_id')
->add('topic_text')
;
}
TopicContent Entity
<?php
namespace Application\ClubBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
class TopicContent
{
/**
*
* #var integer
*/
private $topic_id;
/**
* #var string
*/
private $topic_text;
/**
* #var \Application\ClubBundle\Entity\Topic
*/
private $topic;
/**
* Set topic_id
*
* #param integer $topicId
* #return TopicContent
*/
public function setTopicId($topicId)
{
$this->topic_id = $topicId;
return $this;
}
/**
* Get topic_id
*
* #return integer
*/
public function getTopicId()
{
return $this->topic_id;
}
/**
* Set topic_text
*
* #param string $topicText
* #return TopicContent
*/
public function setTopicText($topicText)
{
$this->topic_text = $topicText;
return $this;
}
/**
* Get topic_text
*
* #return string
*/
public function getTopicText()
{
return $this->topic_text;
}
/**
* Set topic
*
* #param \Application\ClubBundle\Entity\Topic $topic
* #return TopicContent
*/
public function setTopic(\Application\ClubBundle\Entity\Topic $topic = null)
{
$this->topic = $topic;
return $this;
}
/**
* Get topic
*
* #return \Application\ClubBundle\Entity\Topic
*/
public function getTopic()
{
return $this->topic;
}
}
Topic Entity
/**
* Add topic_content
*
* #param \Application\ClubBundle\Entity\TopicContent $topicContent
* #return Topic
*/
public function setTopicContent(\Application\ClubBundle\Entity\TopicContent $topicContent)
{
$this->topic_content[] = $topicContent;
return $this;
}
my entities relatoins
Topic
Application\ClubBundle\Entity\Topic:
type: entity
table: topic
id:
topic_id:
type: integer
generator: { strategy: AUTO }
fields:
topic_title:
type: string
length: 200
oneToMany:
topic_content:
targetEntity: TopicContent
mappedBy: topic
topic_tag:
targetEntity: TopicTag
mappedBy: topic
cascade: ["persist"]
TopicContent
Application\ClubBundle\Entity\TopicContent:
type: entity
table: topic_content
id:
topic_id:
type: integer
fields:
topic_text:
type: text
oneToOne:
topic:
targetEntity: Topic
inversedBy: topic_content
joinColumn:
name: topic_id
referencedColumnName: topic_id
cascade: ["persist"]

Answer 1

You have the answer in the error message displayed by Symfony: you need to persist the Topic entity AND the TopicContent entity. To do that you must define a cascade={"persist"} on the relation.
Edit:
Another way to persist the TopicContent would be to do it explicitly in the form processing function:
if ($form->isValid()) {
$em = $this->getDoctrine()->getManager();
$content = $entity->getTopicContent();
$em->persist($entity);
$em->persist($content);
$em->flush();
return $this->redirect($this->generateUrl('application_club_show', array('id' => $entity->getTopicId())));
}