Symfony 2 实体窗体类型的转换器

我正在尝试在Symfony 2中创建一种新的表单类型。它基于实体类型，它在前端使用 select2，我需要用户能够选择现有实体或创建新实体。

我的想法是发送实体的 ID，如果用户选择现有实体，则让它由默认实体类型转换，或者如果用户输入新值，则发送类似"_new：输入的文本"之类的内容。然后这个字符串应该通过我自己的模型转换器转换为新的表单实体，它应该看起来像这样：

<?php
namespace Acme'MainBundle'Form'DataTransformer;
use Symfony'Component'Form'DataTransformerInterface;
class EmptyEntityTransformer
implements DataTransformerInterface
{
    private $entityName;
    public function __construct($entityName)
    {
        $this->entityName = $entityName;
    }
    public function transform($val)
    {
        return $val;
    }
    public function reverseTransform($val)
    {
        $ret = $val;
        if (substr($val, 0, 5) == '_new:') {
            $param = substr($val, 5);
            $ret = new $this->entityName($param);
        }
        return $ret;
    }
}

遗憾的是，只有在选择现有实体时才会调用转换器。当我输入一个新值时，字符串会在请求中发送，但根本不调用转换器的 reverseTransform 方法。

我是Symfony的新手，所以我甚至不知道这种方法是否正确。您知道如何解决此问题吗？

编辑：我的表单类型代码是：

<?php
namespace Acme'MainBundle'Form'Type;
use Symfony'Component'Form'AbstractType;
use Symfony'Component'Form'FormBuilderInterface;
use Symfony'Component'Form'FormView;
use Symfony'Component'Form'FormInterface;
use Symfony'Bundle'FrameworkBundle'Routing'Router;
use Acme'MainBundle'Form'DataTransformer'EmptyEntityTransformer;
use Symfony'Component'PropertyAccess'PropertyAccess;
use Symfony'Component'OptionsResolver'OptionsResolverInterface;
use Symfony'Component'Form'FormEvent;
use Symfony'Component'Form'FormEvents;
class Select2EntityType
extends AbstractType
{
    protected $router;
    public function __construct(Router $router)
    {
        $this->router = $router;
    }
    /**
     * {@inheritdoc}
     */
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        parent::setDefaultOptions($resolver);
        $resolver->setDefaults(array(
            'placeholder' => null,
            'path' => false,
            'pathParams' => null,
            'allowNew' => false,
            'newClass' => false,
        ));
    }
    public function getParent()
    {
        return 'entity';
    }
    public function getName()
    {
        return 's2_entity';
    }
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        if ($options['newClass']) {
            $transformer = new EmptyEntityTransformer($options['newClass']);
            $builder->addModelTransformer($transformer);
        }
    }
    public function buildView(FormView $view, FormInterface $form, array $options)
    {
        $field = $view->vars['name'];
        $parentData = $form->getParent()->getData();
        $opts = array();
        if (null !== $parentData) {
            $accessor = PropertyAccess::createPropertyAccessor();
            $val = $accessor->getValue($parentData, $field);
            if (is_object($val)) {
                $getter = 'get' . ucfirst($options['property']);
                $opts['selectedLabel'] = $val->$getter();
            }
            elseif ($choices = $options['choices']) {
                if (is_array($choices) && array_key_exists($val, $choices)) {
                    $opts['selectedLabel'] = $choices[$val];
                }
            }
        }
        $jsOpts = array('placeholder');
        foreach ($jsOpts as $jsOpt) {
            if (!empty($options[$jsOpt])) {
                $opts[$jsOpt] = $options[$jsOpt];
            }
        }
        $view->vars['allowNew'] = !empty($options['allowNew']);
        $opts['allowClear'] = !$options['required'];
        if ($options['path']) {
            $ajax = array();
            if (!$options['path']) {
                throw new 'RuntimeException('You must define path option to use ajax');
            }
            $ajax['url'] = $this->router->generate($options['path'], array_merge($options['pathParams'], array(
                'fieldName' => $options['property'],
            )));
            $ajax['quietMillis'] = 250;
            $opts['ajax'] = $ajax;
        }
        $view->vars['options'] = $opts;
    }
}

然后我创建此表单类型：

class EditType
extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('masterProject', 's2_entity', array(
                'label' => 'Label',
                'class' => 'MyBundle:MyEntity',
                'property' => 'name',
                'path' => 'my_route',
                'pathParams' => array('entityName' => 'name'),
                'allowNew' => true,
                'newClass' => '''...''MyEntity',
            ))

。

感谢您的建议