上载图像时出错:调用成员函数guessExtension

我有一个实体代理与实体Photo相关的OneToOne

代理

class Agence
{
   /**
    * @ORM'OneToOne(targetEntity="Project'DashboardBundle'Entity'Photo", cascade={"persist"})
    * @ORM'JoinColumn(nullable=true)
    */
 private $photo;

这是实体照片的简介

<?php
namespace Project'DashboardBundle'Entity;
use Doctrine'ORM'Mapping as ORM;
use Symfony'Component'Validator'Constraints as Assert;

/**
* Photo
*
* @ORM'Table()
* @ORM'Entity(repositoryClass="Project'DashboardBundle'Entity'PhotoRepository")
* @ORM'HasLifecycleCallbacks
*/
class Photo
{
/**
 * @var integer
 *
 * @ORM'Column(name="id", type="integer")
 * @ORM'Id
 * @ORM'GeneratedValue(strategy="AUTO")
 */
private $id;
/**
 * @var string
 *
 * @ORM'Column(name="url", type="string", length=255)
 */
private $url;
 /**
 * @var string
 *
 * @ORM'Column(name="alt", type="string", length=255)
 */
 private $alt;
/**
* @Assert'File(maxSize="1M")
*/
public $file;
  public function setFile($file)
{
$this->file = $file;
if (null !== $this->url) {
  $this->tempFilename = $this->url;
  $this->url = null;
  $this->alt = null;
 }
}
public function getFile()
{
 return $this->file;
}

private $tempFilename;
/**
 * @ORM'PrePersist()
 * @ORM'PreUpdate()
 */
public function preUpload()
{
 if (null === $this->file) {
  return;
}
$this->url = $this->file->guessExtension();
$this->alt = $this->file->getClientOriginalName();
}
/**
* @ORM'PostPersist()
* @ORM'PostUpdate()
*/
public function upload()
{
  if (null === $this->file) {
  return;
}
if (null !== $this->tempFilename) {
  $oldFile = $this->getUploadRootDir().'/'.$this->id.'.'.$this->tempFilename;
  if (file_exists($oldFile)) {
    unlink($oldFile);
  }
}
$this->file->move(
  $this->getUploadRootDir(), 
  $this->id.'.'.$this->url  
 );
}
/**
* @ORM'PreRemove()
*/
public function preRemoveUpload()
{
  $this->tempFilename = $this->getUploadRootDir().'/'.$this->id.'.'.$this->url;
}
/**
 * @ORM'PostRemove()
 */
public function removeUpload()
{
  if (file_exists($this->tempFilename)) {
  unlink($this->tempFilename);
}
}
public function getUploadDir()
{
  return 'uploads/img';
}
protected function getUploadRootDir()
{
  return __DIR__.'/../../../../web/'.$this->getUploadDir();
}
public function getWebPath()
{
  return $this->getUploadDir().'/'.$this->getId().'.'.$this->getUrl();
}

当试图上传照片时，我得到了这个错误：

致命错误异常：错误：对D:''wamp''www''agence''src''Project''DashboardBundle''Entity''Photo.php行135中的非对象调用成员函数guessExtension（）

奇怪的是，同样的代码在另一个实体上运行良好！！

已解决我忘记添加｛｛form_enctype（form）｝｝