我按照官方最新的pdf手册(en Edition)做了一个添加、浏览、更新、删除产品的demo，product里面有一个多对一的category属性，经过之前测试，是没有问题的。
src/Acme/StoreBundle/Entity/Product.php

/**
 * @ORM\ManyToOne(targetEntity="Category", inversedBy="products")
 * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
*/
protected $category;

src/Acme/StoreBundle/Entity/Category.php

/**
 * @ORM\OneToMany(targetEntity="Product", mappedBy="category")
*/
protected $products;

然后按照Form章节，我把添加产品的页面改造成了个表单提交添加产品：

public function createAction(Request $request)
    {
        $category = $this->getDoctrine()
            ->getRepository('AcmeStoreBundle:Category')
            ->find(1);

        $product = new Product();
        $product->setCategory($category);

        $form = $this->createFormBuilder($product)
            ->add('name')
            ->add('price')
            ->add('description')
            ->getForm();

        if($request->getMethod() == 'POST')
        {
            $form->bindRequest($request);

            if($form->isValid())
            {
                $created = true;
                $em = $this->getDoctrine()->getEntityManager();
                $em->persist($product);
                $em->flush();
            }
        }

        return $this->render('AcmeStoreBundle:Default:create.html.twig', array('created' => $created, 'form' => $form->createView(), 'product_id' => $product->getId() ));
    }

到此时所有的环节都可以正常的工作，数据库也可以创建成功数据，然后我看到 “Creating Form Classes”，于是用命令行自带的 doctrine:generate:form 创建了个Form类：

php app/console doctrine:generate:form AcmeStoreBundle:Product

src/Acme/StoreBundle/Form/ProductType.php

namespace Acme\StoreBundle\Form;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;

class ProductType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder
            ->add('name') 
            ->add('price') 
            ->add('description') 
            ->add('category')
        ;
    }

    public function getName()
    {
        return 'acme_storebundle_producttype';
    }
}

然后按照手册上，修改了控制器的代码：

...
use Acme\StoreBundle\Form\ProductType;
...
$form = $this->createForm(new ProductType(), $product);
...

但是清除缓存之后访问地址出现了symfony2的500错误，日志中的错误提示：

[2012-08-26 16:00:27] request.INFO: Matched route "store_create" (parameters: "_controller": "Acme\StoreBundle\Controller\DefaultController::createAction", "_route": "store_create") [] []
[2012-08-26 16:00:27] request.CRITICAL: Symfony\Component\Form\Exception\FormException: Entity "Acme\StoreBundle\Entity\Category" passed to the choice field must have a "__toString()" method defined (or you can also override the "property" option). (uncaught exception) at /work/projects/admin/php/vendor/symfony/src/Symfony/Bridge/Doctrine/Form/ChoiceList/EntityChoiceList.php line 188 [] []

echo输出内容调试之后定位在修改的那句 “ $form = $this->createForm(new ProductType(), $product); ”