php – Symfony2：使用Ajax和jQuery上传文件

这是我的代码：

控制器：

public function createAction(Request $request)
{        
    if ($request->isXmlHttpRequest() && !$request->isMethod('POST')) {
    throw new HttpException('XMLHttpRequests/AJAX calls must be POSTed');
    }

    $entity = new Student();
    $form = $this->createCreateForm($entity);
    $form->handleRequest($request);

    if ($form->isValid()) {
       $file = $entity->getPhoto();

       $fileName = md5(uniqid()).'.'.$file->guessExtension();

       $photoDir = $this->container->getParameter('kernel.root_dir').'/../web/uploads/images';

       $file->move($photoDir,$fileName);

       $entity->setPhoto($fileName);

       $em = $this->getDoctrine()->getManager();
       $em->persist($entity);
       $em->flush();

       if ($request->isXmlHttpRequest()) {
            return new JsonResponse(array('message' => 'Success!','success' => true),200);
        }

        if ($request->isMethod('POST')) {
        return new JsonResponse(array('message' => 'Invalid form','success' => false),400);
    }

      return $this->redirect($this->generateUrl('student_show',array('id' => $entity->getId())));
    }
    return $this->render('BackendBundle:Student:new.html.twig',array(
        'entity' => $entity,'form'   => $form->createView(),));
}

实体：

use DoctrineORMMapping as ORM;
   use SymfonyComponentValidatorConstraints as Assert;

   //...
   /**
   * @var string
   *
   * @ORMColumn(name="photo",type="string",length=255,nullable=true)
   * 
   */
   private $photo;


   public function setPhoto($photo)
   {
    $this->photo = $photo;

    return $this;
   }

   public function getPhoto()
   {
    return $this->photo;
   }

formtype：

//...

   ->add('photo','file',array('required' => false))

   //...

使用Javascript：

//...

$('.form_student').on("submit",function(event) {
 event.preventDefault();

 $.ajax({
  type: 'POST',url: Routing.generate('student_create'),data: $(this).serialize(),dataType: 'json',success: function(response) {

   alert(response.message);
  },error: function (response,desc,err){
      if (response.responseJSON && response.responseJSON.message) {
         alert(response.responseJSON.message);
      }
      else{
         alert(desc);
      }
  }
 });
});

我现在遇到的问题是我必须使用Ajax请求,但不知道如何发送该文件字段,然后可以在Symfony控制器中使用它.

我见过一些FormData(),但不知道它是如何使用的.

你可以帮帮我吗？