How to have the placeholder translated in an EntityType? - forms

Question

I'm building a form which has an EntityType element, the problem I have is that I'm unable to have the placeholder translated.
Here is my code:
$builder
->add('Products', EntityType::class, [
'mapped' => false,
'expanded' => true,
'multiple' => false,
'required' => false,
'class' => Product::class,
'choices' => $options['step']->getProducts(),
'placeholder' => 'form.mat.alreadyOwned',
'label' => 'form.mat.alreadyOwned',
'translation_domain' => 'messages'
])
When I use the form.mat.alreadyOwnedtranslation as the label it works fine, but I would like to use it in the placeholder instead. What am I missing?
Looking forward to any tips or tricks that you have to offer!
[UPDATE]
As pointed out by #gp_sflover I'm not trying to replace the general placeholder, but the one for the empty value. This one only appears if you set required to false.

Answer 1

After some research and thought, the places where the placeholder is actually used are quite limited in number (as it should be). However, specific placeholder translation is not a special case (sadly).
For every choice in a ChoiceType a ChoiceView is added. Also for the placeholder a ChoiceView is added, that inherits the options of the form (which is a somewhat sensible choice for the ChoiceType), including the translation_domain parameter, which indicates that the choices shall be translated (all of them). There's also a reference in some twig template that specifically manages the translation in the twig bridge for non-expanded choice types. However, those don't open up a specific best practices answer on how to specifically handle translations for the placeholder in the ChoiceType.
For the EntityType, this doesn't change.
So there are a few approaches, some of which might be absolutely utility-free ...
translate the placeholder right there when building the form
Although this is conceptually not the most beautiful option, IMHO it's still the most practical one. Essentially, in Symfony 4 forms can receive dependencies in their constructor via auto-wiring, so injecting a TranslatorInterface will open up the ability to translate the placeholder with the requests locale (which is automatically set for the translator via event listener):
public function __construct(TranslatorInterface $translator) {
$this->translator = $translator;
}
and in your buildForm you can then use it to translate the placeholder
$builder
->add('Products', EntityType::class, [
'mapped' => false,
'expanded' => true,
'multiple' => false,
'required' => false,
'class' => Product::class,
'choices' => $options['step']->getProducts(),
'placeholder' => $this->translator->trans('form.mat.alreadyOwned'), // <-- change
'label' => 'form.mat.alreadyOwned',
'translation_domain' => 'messages'
])
not to withhold the other options, which in my opinion are almost all overkill...
set a choice_translation_domain for all entries, including placeholder
obviously, this can and probably will lead to problems, if there ever is an entity that whose choice label matches the key in the translator ... and it is not intended for translation. but it will translate the placeholder with the very same translation_domain ...
adapt the form rendering and check for the placeholder
this is problematic, since you have to assign the form theme/form rendering to all relevant forms. the placeholder does have a unique name ('placeholder', who would have thought) so it could very well be used to achieve that goal. However, setting a different translation domain could very much be challenging. (if you attempt this, it's a bit of a nuisance)
write your own entity type (optionally adding own form rendering)
theoretically, you could create your own EntityType and handle the placeholder properly there. like ... adding a translation domain to the choice view and sub form and what not. For inspiration/reference consult the ChoiceType, EntityType and DoctrineType (parent type).