Symfony custom form

->add('firstname', TextType::class, array('attr' => array('class' => 'form-control')))
            ->add('lastname', TextType::class, array('attr' => array('class' => 'form-control')))
            ->add('class', EntityType::class, array(
                'class' => SchoolClass::class,
                'multiple' => false,
                'attr' => array('class' => 'form-control'),
            ));