title: Django models id issue
body: <p>I'm not able to query a django model.</p>
  
  <p>the model is as follow.</p>
  
  <pre><code>class DeviceLevelMapping(models.Model):
      device = models.ForeignKey(DeviceDetails)
      level1 = models.ForeignKey('Level1Detail')
      level2 = models.ForeignKey('Level2Detail')
      level3 = models.ForeignKey('Level3Detail')
      level4 = models.ForeignKey('Level4Detail')
      level5 = models.ForeignKey('Level5Detail')
      level6 = models.ForeignKey('Level6Detail')
      level7 = models.ForeignKey('Level7Detail')
      class Meta:
          db_table = 'device_level_mapping'
  </code></pre>
  
  <p>When I fire a query <code>DeviceLevelMapping.objects.filter(level1_id = l_id)</code> it says <code>unknown column</code>DeviceLevelMapping.id`. </p>
  
  <p>Where is problem lying?</p>
  
  <p><strong>EDITED</strong></p>
  
  <pre><code>class Level1Detail(models.Model):
      level1_id = models.IntegerField(primary_key=True)
      level1_name = models.CharField(max_length=256L)
      organization = models.ForeignKey('OrganizationDetails')
      class Meta:
          db_table = 'level1_detail'
  </code></pre>