models.py 文件源码

def insertion_target_filters(self, instance, order_insertion_by):
        """
        Creates a filter which matches suitable right siblings for ``node``,
        where insertion should maintain ordering according to the list of
        fields in ``order_insertion_by``.

        For example, given an ``order_insertion_by`` of
        ``['field1', 'field2', 'field3']``, the resulting filter should
        correspond to the following SQL::

           field1 > %s
           OR (field1 = %s AND field2 > %s)
           OR (field1 = %s AND field2 = %s AND field3 > %s)

        """
        fields = []
        filters = []
        fields__append = fields.append
        filters__append = filters.append
        and_ = operator.and_
        or_ = operator.or_
        for field_name in order_insertion_by:
            if field_name[0] == '-':
                field_name = field_name[1:]
                filter_suffix = '__lt'
            else:
                filter_suffix = '__gt'
            value = getattr(instance, field_name)
            if value is None:
                # node isn't saved yet. get the insertion value from pre_save.
                field = instance._meta.get_field(field_name)
                value = field.pre_save(instance, True)

            q = Q(**{field_name + filter_suffix: value})

            filters__append(reduce(and_, [Q(**{f: v}) for f, v in fields] + [q]))
            fields__append((field_name, value))
        return reduce(or_, filters)