Sylius\Bundle\OrderBundle\Form\Type\OrderItemType::buildForm PHP Method

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('quantity', IntegerType::class, ['attr' => ['min' => 1], 'label' => 'sylius.ui.quantity'])->setDataMapper($this->dataMapper);
    }

 /**
  * {@inheritdoc}
  */
 public function buildForm(FormBuilderInterface $builder, array $options)
 {
     parent::buildForm($builder, $options);
     $builder->addEventListener(FormEvents::PRE_SUBMIT, function (FormEvent $event) use($options) {
         $data = $event->getData();
         if (isset($data['variant'])) {
             $event->getForm()->add('variant', 'entity_hidden', array('data_class' => $options['variant_data_class']));
         }
     });
 }