title: Confusion with Queryset.annotate()
body: <p>I have two models:</p>
  
  <pre><code>class Property(models.Model):
      # code here...
  
  class AccommodationType(models.Model):
      property = models.ForeignKey(Property, related_name='accommodation_types')
      # rest of code here...
  </code></pre>
  
  <p>What I'm trying to to is to annotate Property's queryset with count of related AccommodationType's and filter it by the value of this count. So here is my code:</p>
  
  <pre><code>qs = Property.objects.all()
  qs.annotate(acc_types_count=Count('accommodation_types'))
  filtered = qs.filter(acc_types_count=1)
  </code></pre>
  
  <p>and here I got the error:</p>
  
  <pre><code>django.core.exceptions.FieldError: Cannot resolve keyword 'acc_types_count' into field. Choices are:  # ...rest of the fields
  </code></pre>
  
  <p>Where I am wrong?</p>