title: Entity class has no field or association named like in my DB
body: <p>I want to create an request that recovers a number according to e.rules_id, e.status_id</p>
  
  <pre><code>public function findStat() 
  {
   $types = $this-&gt;em
          -&gt;getRepository('EthanRestBundle:EthanRules')
          -&gt;createQueryBuilder('e')
          -&gt;select('e.rules_id, e.status_id, COUNT(*)')
          -&gt;groupBy('e.rules_id, e.status_id')
          -&gt;orderBy('rules_id');
  
      $types = $types-&gt;getQuery()-&gt;getSingleScalarResult();
  
      return $types;
  
  }
  </code></pre>
  
  <p>The error message:</p>
  
  <blockquote>
    <p>[Semantical Error] line 0, col 9 near 'rules_id, e.status_id,': Error: Class Ethan\RestBundle\Entity\EthanRules has no field or association named rules_id"</p>
  </blockquote>
  
  <p>I develop on Symfony 2 with FosrestBundle to create a REST Application</p>