How to mark existing data in output?

Question

symfony

Hello! I have two tables, Users and Roles with a ManyToMany relationship. I just can’t figure out how to make the roles that he already has marked when displaying the user’s form for editing? Here's an example of my buildform... can't figure it out, does anyone know? :)

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

        $builder
            ->add('username')
            ->add('roles', EntityType::class , array(
        'class' => 'AppBundle\Entity\Roles',
                'choice_label'     => 'name',
                'multiple' => true,
                'expanded' => true,
                'mapped' => false,
    ))

        ;
    }