>>> Cat.objects.annotate(nb_friends=models.Count('dog_friends'))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/manager.py", line 122, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/query.py", line 908, in annotate
    clone.query.add_annotation(annotation, alias, is_summary=False)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 987, in add_annotation
    summarize=is_summary)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/aggregates.py", line 19, in resolve_expression
    c = super(Aggregate, self).resolve_expression(query, allow_joins, reuse, summarize)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 509, in resolve_expression
    c.source_expressions[pos] = arg.resolve_expression(query, allow_joins, reuse, summarize, for_save)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/expressions.py", line 466, in resolve_expression
    return query.resolve_ref(self.name, allow_joins, reuse, summarize)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1464, in resolve_ref
    self.get_initial_alias(), reuse)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1405, in setup_joins
    names, opts, allow_many, fail_on_missing=True)
  File "/data/.virtualenvs/bugproxy/local/lib/python2.7/site-packages/django/db/models/sql/query.py", line 1330, in names_to_path
    "Choices are: %s" % (name, ", ".join(available)))
FieldError: Cannot resolve keyword 'dog_friends' into field. Choices are: id, name
>>> Mammal.objects.annotate(nb_friends=models.Count('dog_friends'))
[<Mammal: Mammal object>, <Mammal: Mammal object>]