Ok, in case somebody gets here with the same question, this is what I've done in the end:
I've created a custom field type (see http://symfony.com/doc/current/cookbook/form/create_custom_field_type.html)
Since we is going to be an entity field in the end, you want to add:
public function getParent() {
return 'entity';
}
When using it on the Form:
$builder->add('creditcard', new CreditCardFieldType(),
array( 'label' => 'Credit Card',
'required' => true,
'expanded' => false,
'class' => 'Acme\Bundle\Entity\CreditCardCharge',
'property' => 'object',
'multiple' => false,
'query_builder' => function(\Acme\Bundle\Repository\CreditCardChargeRepository $er) {
return $er->createQueryBuilder('b');
},
'mapped' => false,
));
object is a new property added to the entity that contains the whole object, so I added to the entity:
public function getObject()
{
return $this;
}
This way we can access to the object from the template, we just need to create a new template for our own custom field type:
{% block creditcard_widget %}
{% spaceless %}
{% if required and empty_value is none and not empty_value_in_choices %}
{% set required = false %}
{% endif %}
<select {{ block('widget_attributes') }}{% if multiple %} multiple="multiple"{% endif %}>
{% if empty_value is not none %}
<option value=""{% if required and value is empty %} selected="selected"{% endif %}>{{ empty_value|trans({}, translation_domain) }}</option>
{% endif %}
{% if preferred_choices|length > 0 %}
{% set options = preferred_choices %}
{{ block('choice_creditcard_widget_options') }}
{% if choices|length > 0 and separator is not none %}
<option disabled="disabled">{{ separator }}</option>
{% endif %}
{% endif %}
{% set options = choices %}
{{ block('choice_creditcard_widget_options') }}
</select>
{% endspaceless %}
{% endblock creditcard_widget %}
{% block choice_creditcard_widget_options %}
{% spaceless %}
{% for group_label, choice in options %}
{% if choice is iterable %}
<optgroup label="{{ group_label|trans({}, translation_domain) }}">
{% set options = choice %}
{{ block('choice_creditcard_widget_options') }}
</optgroup>
{% else %}
<option value="{{ choice.data.creditcard }}" charge="{{ choice.data.charge }}" {% if choice is selectedchoice(data.creditcard_charges_id) %} selected="selected"{% endif %}>{{ choice.data.text|trans({}, translation_domain) }}</option>
{% endif %}
{% endfor %}
{% endspaceless %}
{% endblock choice_creditcard_widget_options %}
And register it for twig in your config.yml:
twig:
form:
resources:
- 'AcmeBundle:Form:creditcardfield.html.twig'
Not sure it is the best solution but it does the trick. Hope it helps.