Symfony2 / Twig：如何将允许的值设置为dropDownField

I have 3 Entities: User , Report and ReportCategory. A User can put Reports in ONE ReportCategory. In the User-Entity there is a list, which ReportCategories are allowed for the user. This works all fine - I made it with a connectionTable which has the userID and the reportCategoryId.

Now I make an Array in Controller to get all ReportCategories of the current logged in User:

public function newAction()
    {
        $entity = new Report();
        $form   = $this->createCreateForm($entity);

        $userId = $this->get('security.context')->getToken()->getUser()->getId();
        $user = $this->getDoctrine()->getRepository('MyBundle:User')->find($userId);
        $userReportCategories = array();

        foreach($user->getReportCategories() as $reportCategory)
        {
            $userReportCategories[] = $reportCategory->getId();
        }

        return array(
            'entity' => $entity,
            'form'   => $form->createView(),
            'userReportCategories' => $userReportCategories
        );
    }

How can I set only these Values to my twig template field? When I make an own field it is not managed form Doctrine!

{{ form_row(form.reportCategory, {'attr': {'class': 'form-control'}, 'label': 'Category'}) }}

THANKS FOR ANY HELP!!!

UPDATE: My ReportType looks like this:

class ReportType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('reportCategory')
            ->add('creationDate', 'date', array(
                'data' => new \DateTime()
            ))
            ->add('headline')
            ->add('text')
            ->add('user')

        ;
    }
....

Create a form class and add an event listener so that the form is aware of the user. The following is an adaptation of How to dynamically Generate Forms Based on user Data in the Symfony docs. [It is not guaranteed to accurately capture your needs].

form class

use Symfony\Component\Security\Core\SecurityContext;
use Doctrine\ORM\EntityRepository;
// ...

class ReportFormType extends AbstractType
{
    private $securityContext;

    public function __construct(SecurityContext $securityContext)
    {
        $this->securityContext = $securityContext;
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {


        // grab the user, do a quick sanity check that one exists
        $user = $this->securityContext->getToken()->getUser();
        if (!$user) {
            throw new \LogicException(
                'The ReportFormType cannot be used without an authenticated user!'
            );
        }

        $builder->addEventListener(
            FormEvents::PRE_SET_DATA,
            function (FormEvent $event) use ($user) {
                $form = $event->getForm();

                $formOptions = array(
                    'class' => 'Acme\DemoBundle\Entity\ReportCategory',
                    'property' => 'category',
                    'query_builder' => function (EntityRepository $er) use ($user) {
                        // build a custom query
                        // return $er->createQueryBuilder('c')
                        ->select('category')
                        ->where('user = $user);
                    },
                );

                // create the field, this is similar the $builder->add()
                // field name, field type, data, options
                $form->add('userReportCategories', 'entity', $formOptions);
            }
        );
    }

    // ...
}

new action

public function newAction()
    {
        $entity = new Report();
        $form   = $this->createForm(new ReportFormType(), $entity);

        return array(
            'entity' => $entity,
            'form'   => $form->createView(),
        );
    }