title: Selecting random DB entry in Symfony2 - Getting an error
body: <p>I have been trying to pull out a random row, I have used this: </p>
  
  <p>This is the example code I found which did not really help ( I found here: <a href="https://gist.github.com/pierroweb/1518601" rel="nofollow">https://gist.github.com/pierroweb/1518601</a>)</p>
  
  <pre><code>class QuestionRepository extends EntityRepository
  {
      public function findOneRandom()
      {
          $em = $this-&gt;getEntityManager();
          $max = $em-&gt;createQuery('
              SELECT MAX(q.id) FROM EnzimQuestionBundle:Question q
              ')
              -&gt;getSingleScalarResult();
          return $em-&gt;createQuery('
              SELECT q FROM EnzimQuestionBundle:Question q 
              WHERE q.id &gt;= :rand
              ORDER BY q.id ASC
              ')
              -&gt;setParameter('rand',rand(0,$max))
              -&gt;setMaxResults(1)
              -&gt;getSingleResult();
      }
  }
  </code></pre>
  
  <p>Now I have something like this:</p>
  
  <pre><code>    $em = $this-&gt;getEntityManager();
      $max = $em-&gt;createQuery('SELECT MAX(p.id) FROM GreenMonkeyDevGlassShopBundle:Product p')-&gt;getSingleScalarResult();
      return $em-&gt;createQuery('SELECT p FROM GreenMonkeyDevGlassShopBundle:Product p INNER JOIN (SELECT p2.categories. FROM GreenMonkeyDevGlassShopBundle:Product p.categories WHERE :cid IN(pc) p.id &gt;= :rand ORDER BY p.id ASC')
          -&gt;setParameter('cid', $category_id)
          -&gt;setParameter('rand',rand(0,$max))
          -&gt;setMaxResults(intval($limit))
          -&gt;getSingleResult();
  </code></pre>
  
  <p>I keep getting this error though: 
  <code>FatalErrorException: Error: Call to undefined method Doctrine\ORM\Query\ResultSetMapping::addRootEntityFromClassMetadata() in /var/www/gmd-milkywayglass/src/GreenMonkeyDev/GlassShopBundle/Entity/CategoryRepository.php line 42</code></p>
  
  <p>Any thoughts on what I can be doing wrong? I know that Doctrine does not have a get random method. Maybe there is some simple solution? Thank you!</p>