Symfony 2 实体字段属性

I have in my form an entity field. This field looks like this:

->add('user', 'entity',array(
                                'class' => 'ElearningSiteBundleEntityUser',
                                'property' => 'name',
                                'multiple' => true,
                                'expanded' => true,
                                'required' => true,
                                'label' => 'Użytkownicy ',
                                'attr' => array('class' => 'userFiledCollection'), // this not working. It set class to parent div. I want to have this class in checkboxes.
                                'query_builder' =>function(EntityRepository $er) {
                                                     return $er
                                                        ->createQueryBuilder('u')
                                                        ->where('u.isActive = 1');
                                                      },
                        )
                    )

我要做的就是为该字段呈现的所有复选框设置一个类属性.我该怎么做?

{% form_theme form _self %}

{% block checkbox_widget %}
    {% spaceless %}
        {% set attr = attr|merge({'class': 'userFiledCollection'}) %}
        <input type="checkbox" {{ block('widget_attributes') }}{% if value is defined %} value="{{ value }}"{% endif %}{% if checked %} checked="checked"{% endif %} />
    {% endspaceless %}
{% endblock checkbox_widget %}

{% block body %}
    {{ form(form) }}
{% endblock %}