Symfony2 - How to add a ModelTransformer within FieldExtension? - php

Question

Goal
Custom Formelement written as an Extension of the (Doctrine) Entity Field. The Element is rendered as a Select2 Element with Tagging. This allows to choose multiple items from a list or add a new value. If a new value is added, a new entity with the value as the property shall be created and associated to the underlying model of the formType.
What works
I can successfully render the select2 Element with the available entities.
Problem
The submitted value is a string containing the (unique) selected properties which currently causes a validation error (invalid value). It doesn't deliever the ID of the selected entities as the original field does, so I wrote a generic DataTransformer that should be able to deal with it. However I am unable to attach the transformer to the field as intended from the context of the TypeExtension. I would have to add the transformer inside my form. As another option I considered is to suppress the validation Listener enitrely, but this would not only disable the validation of the enitre form, it wouldn't be helpful in correctly mapping the selected values to the enitities.
What's the best way to implement this functionality? As the entity FieldType already offers most of the functionality, I would rather try to avoid to write a completly new fieldType.
Update: Why I can't attach the transformer
One option would of course be to do it just the way the cookbook entry suggests, that is to attach the transformer whenever I use the field:
class MyFormType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
// ...
$entityManager = $options['em'];
$transformer = new ObjectListToStringTransformer($this->em,
[
'class' => $options['class'],
'property' => $options['property'],
'delimiter' => ','
]
);
$builder->add(
$builder->create('entityType', 'entity',
array(
'select2' => true, /*Triggers the select2 template to be used*/
'multiple' => true,
'class' => 'Bundle:Entity',
'property' => 'name'
)
)->addModelTransformer($transformer)
);
}
// ....
}
That could work. But this is not verbose and not typesafe. If I set select2 => true the Transformer must be added otherwise it will not validate. So I'd really like to have that done within my Extension. My first approach to achieve this was simply wrong, just the way the cookbook entry mentioned "how NOT to do it":
public function buildForm(FormBuilderInterface $builder, array $options)
{
if ($options['select2']) {
$builder->addModelTransformer(new ObjectListToStringTransformer($this->em,
[
'class' => $options['class'],
'property' => $options['property'],
'delimiter' => ','
]
)
);
}
parent::buildForm($builder, $options);
}
This will add a transformer to the entire form, not only this field. AFAIK I can't do create(...)->addModelTransformer($transformer) as I probably could if it was a sub class (vertical inheritance) but not inside the extension (horizontal inheritance). Is there a way to add it after the field was already added? Or is there a way to achieve this by creating a subclass of the choice field?

Answer 1

Apparently the entity field itself has a registered ModelTransformer (or a ViewTransformer) which get called before my ModelTransformer. Since this always fails, my Transformer is never reached. To get around this, I changed addModelTransformer to addViewTransformer. While the code of my transformer wasn't working yet, the interaction with it does.