title: Doctrine 2 - How to use discriminator column in where clause
body: <p>I was used discriminator column in where clause like this:</p>
  
  <pre><code>//f = root entity
  $qb = $this-&gt;createQueryBuilder('f');
  $qb-&gt;add('where', 'f.format = \'image\' OR f.format = \'text\'');
  </code></pre>
  
  <p>I've got an error: "Message: [Semantical Error] line 0, col 73 near 'format = 'image'': Error: Class Entities\File\AbstractFile has no field or association named format"</p>
  
  <p>How can i use discriminator column in where clause?</p>
  
  <p>Thanks.</p>