title: Query with EXISTS for Doctrine Symfony2
body: <p>How can I implement the following query with Query Builder?</p>
  
  <pre><code>SELECT * 
  FROM t 
  WHERE t.status = 1
      OR EXISTS(SELECT * 
                FROM r 
                WHERE r.t_id = t.id 
                    AND r.status = 1
               )
  </code></pre>
  
  <p>The part without exist check is easy, but is there a way to implement the <code>EXISTS</code>?</p>