Using querysets as an rvalue in filter() calls was causing an unnecessary

        obj = self.values("pk")

        return obj.query.as_nested_sql()

    # When used as part of a nested query, a queryset will never be an "always

    # empty" result.

    value_annotation = True

class ValuesQuerySet(QuerySet):

    def __init__(self, *args, **kwargs):

        super(ValuesQuerySet, self).__init__(*args, **kwargs)

        # (it raises StopIteration immediately).

        yield iter([]).next()

    # EmptyQuerySet is always an empty result in where-clauses (and similar

    # situations).

    value_annotation = False

def get_cached_row(klass, row, index_start, max_depth=0, cur_depth=0,

                   requested=None):

        # here in the future (using Python types is suggested for consistency).

        if isinstance(value, datetime.datetime):

            annotation = datetime.datetime

        elif hasattr(value, 'value_annotation'):

            annotation = value.value_annotation

        else:

            annotation = bool(value)

>>> Annotation.objects.filter(notes__in=Note.objects.filter(note="n1"))

[<Annotation: a1>]

Nested queries should not evaluate the inner query as part of constructing the

SQL. This test verifies this: if the inner query is evaluated, the outer "in"

lookup will raise an EmptyResultSet exception (as the inner query returns

nothing).

>>> print Annotation.objects.filter(notes__in=Note.objects.filter(note="xyzzy")).query

SELECT ...

"""}

# In Python 2.3 and the Python 2.6 beta releases, exceptions raised in __len__