[symfony/Form] Formクラス内で、別フィールドの値を受け取る方法に関する考え

class LifeActivityLogFormType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $entity = $options['data'] ?? null;

        $builder
            ->add('name', TextType::class, [
                'empty_data' => '',
            ])
            ->add('has_checked', CheckboxType::class, [
                'required' => false,
                'label' => false,
            ])
            ->add('life_activity_category', EntityType::class, [
                'label' => 'カテゴリ',
                'class' => LifeActivityCategory::class,
                'empty_data' => '1',
            ])
            ->add('_key', HiddenType::class, [
                'data' => (empty($entity) ? null : $entity->getCode()),
                'mapped' => false,
            ]) 
        ;
    }
}

{{ form._key.vars.value }}