Symfony 2 - Form collection for one entity without parent entity - forms

Question

I have problem with form collection. I want to show one form with all values from one entity and I want to be able to add or remove some record(line) from this entity on one page. I have the following solutions, which is ok.
CurrencyController
class CurrencyController extends Controller {
/**
* #Template()
*/
public function testAction() {
$em = $this->getDoctrine()->getManager();
$currencies = $em->getRepository('MyWebBundle:Currency')->findAll();
$arr = array('currencies' => $currencies);
$form = $this->createFormBuilder($arr)
->add('currencies', 'collection', array(
'type' => new CurrencyType(),
'allow_add' => true,
'allow_delete' => true,
'by_reference' => false,
))
->add('submit', 'button', array('label' => 'Odeslat'))
->getForm();
return array(
'form' => $form->createView(),
);
}
}
CurrencyType
class CurrencyType extends AbstractType {
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options) {
$builder
->add('abbreviation', 'text')
->add('rate', 'number')
;
}
/**
* #param OptionsResolverInterface $resolver
*/
public function setDefaultOptions(OptionsResolverInterface $resolver) {
$resolver->setDefaults(array(
'data_class' => 'My\WebBundle\Entity\Currency'
));
}
/**
* #return string
*/
public function getName() {
return 'currency';
}
}
Twig
{% extends '::base.html.twig' %}
{% block body -%}
<h1>Test</h1>
{{ form(form) }}
{% endblock %}
If I use form class for CurrenciesType, then Symfony throws exception
Notice: Object of class My\WebBundle\Entity\Currency could not be converted to int in
....\web\vendor\symfony\symfony\src\Symfony\Component\
Form\Extension\Core\ChoiceList\ChoiceList.php line 462
Code for this is below.
CurrencyController
class CurrencyController extends Controller {
/**
* #Template()
*/
public function testAction() {
$em = $this->getDoctrine()->getManager();
$currencies = $em->getRepository('MyWebBundle:Currency')->findAll();
$arr = array('currencies' => $currencies);
$form = $this->createForm(new CurrenciesType(), $arr);
return array(
'form' => $form->createView(),
);
}
}
CurrenciesType
class CurrenciesType extends AbstractType {
/**
* #param FormBuilderInterface $builder
* #param array $options
*/
public function buildForm(FormBuilderInterface $builder, array $options) {
$builder
->add('currencies', 'collection', array(
'type' => new CurrencyType(),
'allow_add' => true,
'allow_delete' => true,
'by_reference' => false,
))
->add('submit', 'button', array('label' => 'Send'))
;
}
/**
* #param OptionsResolverInterface $resolver
*/
public function setDefaultOptions(OptionsResolverInterface $resolver) {
$resolver->setDefaults(array(
'data_class' => null
));
}
/**
* #return string
*/
public function getName() {
return 'my_webbundle_currencies';
}
}
CurrencyType and Twig are same as above.
I found solution these solution #1 solution #2, but my symfony still throws exception as above and I don't see different in my solution and these solutions. Please help with this problem. Thank you all :)