title: How to convert this to Doctrine 2 QueryBuilder format?
body: <p>I would like to write nested query with Doctrine; Sample SQL is like below:</p>
  
  <pre><code>SELECT * FROM layer WHERE layer.id NOT IN 
                 (SELECT task_id FROM users_tasks WHERE user_id = 1) 
  AND parent_id IS NOT NULL AND leaf IS TRUE
  </code></pre>
  
  <p>I have problem converting the <strong>SECOND</strong> <code>SELECT</code> statement.</p>
  
  <p>Thanks in advance. </p>
  
  <p>I would like to make it with <code>createQueryBuilder</code> not <code>createQuery</code>.</p>