title: How to safely & remove this associated entity, or set the ID null
body: <p>[Using Symfony2 &amp; Doctrine]</p>
  
  <p>I have two classes</p>
  
  <pre><code>/* AppBundle\Entity\AccessToken
  
      /**
       * @ORM\ManyToOne(targetEntity="AppBundle\Entity\User)
       */
      protected $user;
  </code></pre>
  
  <p>and <code>AppBundle\Entity\User</code>, which contains no references to <code>AppBundle\Entity\AccessToken</code>. I get the famous parent conflict error from symfony attempting to delete a persisted User object. </p>
  
  <p>Is there a way I can easily remove these access tokens, or set the user_id NULL without manually looping through my entities? </p>
  
  <p>On a bidirectional association I can use cascade. I can't figure out what to do here. </p>
  
  <p>Any thoughts?</p>