title: Related Field got invalid lookup: icontains
body: <p>I am trying to include a search field inside my home page. It works for some of the module field. My problem is when I use a ForeignKey field (correct me please if I am wrong).</p>
  
  <p><strong>models.py</strong></p>
  
  <pre><code>class Location(models.Model):
      user = models.ForeignKey(User, on_delete=models.CASCADE)
      my_location = models.CharField(max_length=120, choices=LOCATION_CHOICES)
      update_date = models.DateField(auto_now=True, null=True)
  
      def __str__(self):
          return self.my_location
  
  
  class UserProfile(models.Model):
  
      user = models.ForeignKey(User)
      # The additional attributes we wish to include.
      user_base = models.CharField(max_length=120, choices=LOCATION_CHOICES)
      user_position = models.CharField(max_length=120)
      user_phone = models.PositiveIntegerField()
  
      def __unicode__(self):
          return self.user.username
  </code></pre>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def search_by_location(request):
      if 'q' in request.GET and request.GET['q']:
          q = request.GET['q']
          locations = Location.objects.filter(my_location__icontains=q).order_by('-update_date')
      else:
          locations = Location.objects.order_by('-update_date')
  context = {'locations': locations}
  return render(request, 'index.html', context)
  </code></pre>
  
  <p>My problem is if I use <code>user</code> inside the filter query instead of <code>my_location</code> I receive the error:</p>
  
  <blockquote>
    <p>Related Field got invalid lookup: icontains</p>
  </blockquote>
  
  <p>Please any advice on how to troubleshoot or any documentation I can read.</p>