如何使用EventListener更新相關實體？

Question

創建事件偵聽器Post實體preUpdate，觸發很好，但是當我嘗試更新相關實體Category，它拋出一個錯誤：

Field "category" is not a valid field of the entity "BW\BlogBundle\Entity\Post" in PreUpdateEventArgs. 

我的事件監聽器代碼：

public function preUpdate(PreUpdateEventArgs $args) { 
    $entity = $args->getEntity(); 
    $em = $args->getEntityManager(); 

    if ($entity instanceof Post) { 
     $args->setNewValue('slug', $this->toSlug($entity->getHeading())); // work fine 
     $args->setNewValue('category', NULL); // throw an error 
     // other code... 

我的帖子實體代碼：

/** 
* Post 
* 
* @ORM\Table(name="posts") 
* @ORM\Entity(repositoryClass="BW\BlogBundle\Entity\PostRepository") 
*/ 
class Post 
{ 

    /** 
    * @var string 
    * 
    * @ORM\Column(name="slug", type="string", length=255) 
    */ 
    private $slug; 

    /** 
    * @var integer 
    * 
    * @ORM\ManyToOne(targetEntity="\BW\BlogBundle\Entity\Category") 
    * @ORM\JoinColumn(name="category_id", referencedColumnName="id") 
    */ 
    private $category; 

    // other code 

如何更新此Category實體在這個EvenetListener中與Post實體一樣在我的例子中？

This answer work，but only for Post changes。但我也需要改變Category實體的一些值，比如：

$entity->getCategory()->setSlug('some-category-slug'); // changes not apply, nothing happens with Category entity. 

Answer 1

我猜方法setNewValue只適用於已經改變的字段。也許你的類別已經是NULL。這就是它拋出錯誤的原因。以下是documentation的示例代碼。

/** 
    * Set the new value of this field. 
    * 
    * @param string $field 
    * @param mixed $value 
    */ 
public function setNewValue($field, $value) 
{ 
    $this->assertValidField($field); 

    $this->entityChangeSet[$field][1] = $value; 
} 

/** 
    * Assert the field exists in changeset. 
    * 
    * @param string $field 
    */ 
private function assertValidField($field) 
{ 
    if (! isset($this->entityChangeSet[$field])) { 
     throw new \InvalidArgumentException(sprintf(
      'Field "%s" is not a valid field of the entity "%s" in PreUpdateEventArgs.', 
      $field, 
      get_class($this->getEntity()) 
     )); 
    }