Fixed #7823 -- Fixed an edge case in RelatedField.get_db_prep_lookup() so that

            # that object. In certain conditions (especially one-to-one relations),

            # the primary key may itself be an object - so we need to keep drilling

            # down until we hit a value that can be used for a comparison.

            v = value

            v, field = value, None

            try:

                while True:

                    v = getattr(v, v._meta.pk.name)

                    v, field = getattr(v, v._meta.pk.name), v._meta.pk

            except AttributeError:

                pass

            if field:

                if lookup_type in ('range', 'in'):

                    v = [v]

                v = field.get_db_prep_lookup(lookup_type, v)

                if isinstance(v, list):

                    v = v[0]

            return v

        if hasattr(value, 'as_sql'):

            return QueryWrapper(('(%s)' % sql), params)

        if lookup_type == 'exact':

            return [pk_trace(value)]

        if lookup_type == 'in':

        if lookup_type in ('range', 'in'):

            return [pk_trace(v) for v in value]

        elif lookup_type == 'isnull':

            return []