title: Symfony findBy DATEDIFF
body: <p>I am trying to get all the entries that are having a date bigger than 4 weeks like this</p>
  
  <pre><code>$oRepoArticleImage-&gt;findBy(array('deletedAt' =&gt; 'DATEDIFF(now(), deletedAt) &gt; 4'));
  </code></pre>
  
  <p>I am getting the following error. What I am doing wrong? </p>
  
  <blockquote>
    <p>PHP Fatal error:  Call to a member function format() on a non-object
    in
    .../vendor/doctrine/dbal/lib/Doctrine/DBAL/Types/DateTimeType.php
    on line 53</p>
  </blockquote>