How to show on the select only specific records when it's generated by buildForm for ManyToOne association

Question

I have Entity like this

class User implements UserInterface
{

    // ...

    /**
     * Many Departments have One Central Department (User)
     * @ORM\ManyToOne(targetEntity="User")
     */
    private $centralDepartment;

    // ...
}

with self-referencing association. In related buildForm I use

class UserType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
// ...
                ->add('centralDepartment');
// ...
    }
}

and it creates in my view select list with list of Users. It's correct.

But the goal is to show on the list only Users with specific Role. If there is possibility I want also to validate before saving in database if selected User has specific Role.

Should I use option choice_loader from https://symfony.com/doc/3.4/reference/forms/types/choice.html or is there some better option in Symfony? I tried to change at first the label using

->add('centralDepartment', ChoiceType::class, array('label' => 'Choose Central Department'));

But my select list is empty now.

Answer 1

Going by @Joe suggestion I used EntityType

->add('centralDepartment', EntityType::class, array(
                    'class' => 'AppBundle:User',
                    'query_builder' => function(UserRepository $er) {
                            return $er->findAllBC(true);
                        }   
            ));

where findAllBC(true) is my method in UserRepository to return Query Builder object which included specific Users for my use:

public function findAllBC($returnQB = false)
{
    $qb = $this->createQueryBuilder('u')
        ->andWhere('u.roles LIKE :role')
        ->setParameter('role', '%BC%');

    if(!$returnQB) return $qb->getQuery()->execute();
    else return $qb;
}