Controller - No access in class - Entity - symfony

Question

I got this error message, but I don't really understand why.
Neither the property "categories" nor one of the methods "addCategory()"/"removeCategory()", "setCategories()", "categories()", "__set()" or "__call()" exist and have public access in class "Checkout\Bundle\ItemBundle\Entity\Item".
The thing is, in my entity "Item" I really have all of this stuff:
/**
* #ORM\ManyToMany(targetEntity="Checkout\Bundle\ItemBundle\Entity\Category", mappedBy="items")
**/
private $categories;
and
/**
* Add categories
*
* #param Category $categories
* #return Item
*/
public function addCategory(Category $categories)
{
$this->categories[] = $categories;
return $this;
}
/**
* Remove categories
*
* #param Category $categories
*/
public function removeCategory(Category $categories)
{
$this->categories->removeElement($categories);
}
/**
* Get categories
*
* #return \Doctrine\Common\Collections\Collection
*/
public function getCategories()
{
return $this->categories;
}
Okay, okay - and what is in my Controller?
/**
* Creates a new Item entity.
*
* #Route("/create", name="item_create")
* #param Request $request
* #return \Symfony\Component\HttpFoundation\Response
*/
public function createAction(Request $request)
{
$entity = new Item();
$currentUser = $this->getUser();
$form = $this->createFormBuilder($entity)
->add('name', null, array(
'label' => 'Item Name',
'required' => true,
))
->add('categories', 'entity', array(
'label' => 'Select a Category',
'required' => false,
'class' => 'CheckoutItemBundle:Category',
'property' => 'name',
'query_builder' => function (EntityRepository $er) use ($currentUser) {
return $er->createQueryBuilder('c')
->where('c.user = :user')
->setParameter('user', $currentUser);
},
))
->add('submit', 'submit', array('label' => 'Speichern'))
->getForm();
$form->handleRequest($request);
if ($form->isSubmitted() && $form->isValid()) {
$em = $this->getDoctrine()->getManager();
$em->persist($entity);
$em->flush();
}
return $this->render(
'CheckoutItemBundle:Item:create.html.twig',
array(
'entity' => 'entity',
'form' => $form->createView()
)
);
}
So, the big question is, why he say that he didn't find it, when it is obviously there. Any idea? Thank you in advance!

Answer 1

->add('categories', 'entity', array(
'label' => 'Select a Category',
'required' => false,
'class' => 'CheckoutItemBundle:Category',
'property' => 'name',
'multiple' => true,
'query_builder' => function (EntityRepository $er) use ($currentUser) {
return $er->createQueryBuilder('c')
->where('c.user = :user')
->setParameter('user', $currentUser);
},
))
You have a Many-To-Many relation, but your form expects a Many-To-One. To fix this behavior need to set multiple to true.