使用删除方法时出现数据库错误异常

我正在关注 http://framework.zend.com/manual/current/en/in-depth-guide/data-binding.html

我有以下代码

邮政服务.php：

namespace Blog'Service;
use Blog'Mapper'PostMapperInterface;
use Blog'Model'PostInterface;

class PostService implements PostServiceInterface
{
protected $postMapper;
public function __construct(PostMapperInterface $postMapper)
{
    $this->postMapper = $postMapper;
}
public function findAllPosts() {
    return $this->postMapper->findAll();
}
public function findPost($id) {
    return $this->postMapper->find($id);
 }
public function savePost(PostInterface $post)
 {
     return $this->postMapper->save($post);
 }
 public function deletePost(PostInterface $post)
 {
     return $this->postMapper->delete($post);
 }
}

删除控制器.php

namespace Blog'Controller;
use Blog'Service'PostServiceInterface;
use Zend'Form'FormInterface;
use Zend'Mvc'Controller'AbstractActionController;
use Zend'View'Model'ViewModel;
use Zend'Debug'Debug;
class DeleteController extends AbstractActionController
{
     protected $postService;
   public function __construct(PostServiceInterface $postService) {
    $this->postService = $postService;
}
public function deleteAction()
{
    try {
         $post = $this->postService->findPost($this->params('id'));
     } catch ('InvalidArgumentException $e) {
         return $this->redirect()->toRoute('post');
     }
     $request = $this->getRequest();

     var_dump($_SERVER['REQUEST_METHOD']);

     if ($request->isPost()) {
         $del = $request->getPost('delete_confirmation', 'no');
           if ($del === 'yes') {
             $this->postService->deletePost($post);
           }
           return $this->redirect()->toRoute('post');
         }


     return new ViewModel(array(
         'post' => $post
     ));

   }
 }

ZendDbSqlMapper.php（保存和删除映射部分）

namespace Blog'Mapper;
use Blog'Model'PostInterface;
use Zend'Db'Adapter'AdapterInterface;
use Zend'Db'Adapter'Driver'ResultInterface;
use Zend'Db'ResultSet'ResultSet;
use Zend'Db'ResultSet'HydratingResultSet; /*used directly below*/
use Zend'Db'Sql'Delete;
use Zend'Db'Sql'Insert;
use Zend'Db'Sql'Sql;
use Zend'Db'Sql'Update;
use Zend'Stdlib'Hydrator'HydratorInterface;
use Zend'Db'Sql'PreparableSqlInterface;
class ZendDbSqlMapper implements PostMapperInterface{
protected $dbAdapter;
protected $hydrator;
protected $postPrototype;
public function __construct(AdapterInterface $dbAdapter,HydratorInterface $hydrator,PostInterface $postPrototype) {
    $this->dbAdapter = $dbAdapter;
    $this->hydrator = $hydrator;
    $this->postPrototype = $postPrototype;
}
public function save(PostInterface $postObject)
{
    $postData = $this->hydrator->extract($postObject);
    unset($postData['id']);
    if($postObject->getId())
    {
        $action = new Update('posts');
        $action->set($postData);
        $action->where(array('id = ?'=>$postObject->getId()));
    }
    else
    {
        $action = new Insert('posts');
        $action->values($postData);
    }

     $sql = new Sql($this->dbAdapter);
     $stmt = $sql->prepareStatementForSqlObject($action);
     $result = $stmt->execute();


     if($result instanceof ResultSetInterface)
     {
         if($newId = $result->getGeneratedValue())
         {
             $postObject->setId($newId);
         }
         return $postObject;
     }
     throw new 'Exception('Database error in ZendDbSqlMapper.php');
 }
public function delete(PostInterface $postObject)
{
     $action = new Delete('posts');
     $action->where(array('id = ?' => $postObject->getId()));
     $sql    = new Sql($this->dbAdapter);
     $stmt   = $sql->prepareStatementForSqlObject($action);
     $result = $stmt->execute();
     return (bool)$result->getAffectedRows();
   }
}

删除.phtml

<h1>DeleteController::deleteAction()</h1>
<p>
 Are you sure that you want to delete
 '<?php echo $this->escapeHtml($this->post->getTitle()); ?>' by
 '<?php echo $this->escapeHtml($this->post->getText()); ?>'?
</p>
<form action="<?php echo $this->url('post/delete', array(), true); ?>" method="post">
 <input type="hidden" name="id" value="<?php echo $post->getId(); ?>">
 <input type="submit" name="delete_confirmation" value="yes">
 <input type="submit" name="delete_confirmation" value="no">
</form>

问题：当我尝试在浏览器中删除博客时，例如http://www.myzend.com/blog/delete/2，它显示错误，例如

ZendDbSqlMapper中的数据库错误.php

我尝试了所有方法，但找不到哪里出了问题。

我正在使用Zend framework 2.3.3

如果需要，我可以添加更多详细信息。