symfony 2.7.4 + doctrine/orm 2.4.8 =无法猜测如何从请求信息中获取doctrine实例

我有这个:src/app/config/routing.yml

app_block_edit:
    path: /edit
    defaults: { _controller: AppBundle:Default:edit }
    methods: [GET, POST]

src/AppBundle/Controller/DefaultController.php(仅用于编辑控制器的代码)

public function editAction(Block $block, Request $request)
{
    $editForm = $this->createForm(new BlockType(), $block);
    $editForm->handleRequest($request);
    if ($editForm->isSubmitted() && $editForm->isValid()) {
        return $this->redirectToRoute('app_block_edit', array('id' => $block->getId()));
    }
    return $this->render('admin/edit.html.twig', array(
      'block'       => $block,
      'edit_form'   => $editForm->createView(),
    ));
}

src/AppBundle/实体/Block.php

class Block
{
    private $id;
    private $title;
    private $content;
.
.
.

src/AppBundle/资源/config/理论/Block.orm。yml映射

AppBundle'Entity'Block:
type: entity
table: block
id:
    id:
        type: integer
        generator:
            strategy: AUTO
fields:
    title:
        type: string
    content:
        type: text

访问localhost:8000/edit?id=node_id对于我的节点，我得到这个:

无法猜测如何从请求信息中获取Doctrine实例。500内部服务器错误- LogicException

我不明白为什么。我的课很简单，表格也很简单。有人可以向我解释为什么symfony_demo工作，而我的例子没有?谢谢你。