title: Django error Related Field got invalid lookup: icontains
body: <p>Iam doing a Search in django using foreign key but it shows this error "Related Field got invalid lookup: icontains" i found similar cases here, but didnt work, i think the error is in the views.py in the queryset_list line..</p>
  
  <p>models.py</p>
  
  <pre><code>class Anos_dos_manuais(models.Model):
      ano = models.CharField(max_length=200)
      publicado = models.BooleanField(default=True)
  
  class Meta:
      verbose_name = 'Ano do manual'
      verbose_name_plural = 'Anos dos manuais'
  
  def __str__(self):
      return self.ano
  
  class Disciplina(models.Model):
      título = models.CharField(max_length=200)
      publicado = models.BooleanField(default=True)
  
  class Meta:
      verbose_name = 'Disciplina'
      verbose_name_plural = 'Disciplinas'
  
  def __str__(self):
      return self.título
  
  class Manuais(models.Model):
      nome = models.CharField(max_length=200, null=True)
      título = models.ForeignKey(Disciplina, on_delete=models.DO_NOTHING)
      descrição = RichTextUploadingField(blank=False)
      ano = models.ForeignKey(Anos_dos_manuais, on_delete=models.DO_NOTHING ,max_length=20, null=True, blank=True)
      imagem = models.ImageField(upload_to='imagens/%Y/%m/%d/')
      manual_pdf = models.FileField(upload_to="manuais/%Y/%m/%d", null=True, blank=False)
      data_publicada = models.DateTimeField(default=datetime.now, blank=False, null=True)
      publicado = models.BooleanField(default=True)
  
  class Meta:
      verbose_name = 'Manual'
      verbose_name_plural = 'Manuais'
  
  def __str__(self):
      return self.nome
  </code></pre>
  
  <p>When doing the search with the foreign and icontains it doesnt work, but with other fields it works
  views.py</p>
  
  <pre><code>def search_manual(request):
      queryset_list = Manuais.objects.order_by('-data_publicada')
      disciplinas = Disciplina.objects.filter(publicado=True)
      anos = Anos_dos_manuais.objects.filter(publicado=True)
  
  #keywords
  if 'keywords' in request.GET:
      keywords = request.GET['keywords']
      if keywords:
          queryset_list = queryset_list.filter(título__icontains=keywords)
  
  #Ano
  if 'manual_ano' in request.GET:
      manual_ano = request.GET['manual_ano']
      if manual_ano:
          queryset_list = queryset_list.filter(ano__icontains=manual_ano)
  
  #Disciplina
  if 'manual_disciplina' in request.GET:
      manual_disciplina = request.GET['manual_disciplina']
      if manual_disciplina:
          queryset_list = queryset_list.filter(título__icontains=manual_disciplina)
  
  
  context = {
      'anos': anos,
      'disciplinas': disciplinas,
      'manuais': queryset_list
  }
  return render(request, 'manuais/search.html', context)
  </code></pre>