title: Sonata Admin Bundle - Custom field with URL
body: <p>Is there way to show url with filter to another entity list instead of showing all related entities? </p>
  
  <p>My entity has OneToMany reference to it's events:</p>
  
  <pre><code>/**
   *
   * @ORM\OneToMany(targetEntity="Event", mappedBy="organizer", cascade={"ALL"})
   */
  private $events;
  </code></pre>
  
  <p>$formMapper->add('events') shows me select2 input with all events.</p>
  
  <p>I just want to show a link to events list with filter to current owner.</p>
  
  <p>I'm using Symfony 2.5.</p>