Exception with database error while using delete method

I am following http://framework.zend.com/manual/current/en/in-depth-guide/data-binding.html

I have below code

PostService.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);
 }
}

DeleteController.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 (save and delete mapping part)

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();
   }

}

delete.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>

Problem: When I am trying to delete a blog in browser like http://www.myzend.com/blog/delete/2,it shows error like

Database error in ZendDbSqlMapper.php

I tried everything but could not find where it goes wrong.

I am using Zend framework 2.3.3

I can add more details if needed.