Add attribute to form widget not work - php

Question

I'm trying to add the selected attribute to my <option> tags
{% for product in form.products %}
{# of course this should only done inside a if,
but for testing purpose, it's okay #}
{{ form_widget(product, { 'attr': {'selected': 'selected'} }) }}
{% endfor %}
However this does not work. Even exactly the same copy&paste from the symfony2 docs here does not work: http://symfony.com/doc/current/book/forms.html#rendering-each-field-by-hand
I'm adding the form element inside a FormType à la:
public function buildForm(FormBuilderInterface $builder, array $options) {
parent::buildForm($builder, $options);
$builder
->add('products', 'entity', array('attr' => array('class' => 'choseable input-xlarge'),
'property_path' => false, 'label' => 'form.products.title', 'class' => 'Test\Bundle\Entity\Product', 'choices' => $products, 'multiple' => true, 'empty_value' => 'form.products.placeholder'));
}
All variables ($products) are ok in the example above.
Is there a problem?
I'm using Symfony 2.1.9-dev.

Answer 1

Can you update the question with form creation code? I'm pretty sure that Symfony is able to make item selected only if it's present in your model. But since you field is marked with property_path => false I don't think you can override this behavior...
An idea:
Fetch all the data used in your entity field type and pass it to form object (either via constructor or options array)
Add field as you're currently doing it
Invoke setData right afterwards to set field data (using data fetched in step #1)
Btw, I am not big fan of setData but situation like this just calls for it :)
Hope that this helps...

Answer 2

There are several issues with your code. I reformatted the code below for better clarity.
public function buildForm(FormBuilderInterface $builder, array $options) {
parent::buildForm($builder, $options);
$builder->add('products', 'entity', array(
'attr' => array('class' => 'choseable input-xlarge'),
'property_path' => false,
'label' => 'form.products.title',
'class' => 'Test\Bundle\Entity\Product',
'choices' => $products,
'multiple' => true,
'empty_value' => 'form.products.placeholder'
));
}
Don't use class inheritance for form types (except of course extending AbstractType). Use getParent() for extending other types instead.
You can't set attributes of <option> tags manually. You would have to render the tags by hand.
For marking choices as selected, you need to pass default data to the field. Usually getProducts() would be called here to get the defaults, but you disabled that by setting property_path to false. So you should set the defaults manually by using the data option. Note that the defaults need to be an array/a collection, since multiple is true.
You are manually passing choices, which is a bad practice. If you just remove this option, the entity field can itself query the choices from the DB and optimize the needed statements for better performance.
Format your code. Really. :P