title: Unsupported lookup 'istartwith' for CharField or join on the field not permitted
body: <p>I created some models using Django ORM.</p>
  
  <pre><code>class feed(models.Model):
      location = models.OneToOneField('feedlocation')
  
  class feedlocation(models.Model):
      areaHash = models.CharField(max_length=100,default='')
  </code></pre>
  
  <p>Then I used the follow code to find out the 'feed' on the same areaHash.</p>
  
  <pre><code>Feed.objects.filter(location__areaHash__istartwith='*****')
  </code></pre>
  
  <p>The I got this error:</p>
  
  <pre><code>FieldError: Unsupported lookup 'istartwith' for CharField or join on the field not permitted.
  </code></pre>
  
  <p>What should I do to achieve this query?</p>