models.py 文件源码

def get_ordered_insertion_target(self, node, parent):
        """
        Attempts to retrieve a suitable right sibling for ``node``
        underneath ``parent`` (which may be ``None`` in the case of root
        nodes) so that ordering by the fields specified by the node's class'
        ``order_insertion_by`` option is maintained.

        Returns ``None`` if no suitable sibling can be found.
        """
        right_sibling = None
        # Optimisation - if the parent doesn't have descendants,
        # the node will always be its last child.
        if parent is None or parent.get_descendant_count() > 0:
            opts = node._mptt_meta
            order_by = opts.order_insertion_by[:]
            filters = self.insertion_target_filters(node, order_by)
            if parent:
                filters = filters & Q(**{opts.parent_attr: parent})
                # Fall back on tree ordering if multiple child nodes have
                # the same values.
                order_by.append(opts.left_attr)
            else:
                filters = filters & Q(**{opts.parent_attr: None})
                # Fall back on tree id ordering if multiple root nodes have
                # the same values.
                order_by.append(opts.tree_id_attr)
            queryset = node.__class__._tree_manager.db_manager(node._state.db).filter(filters).order_by(*order_by)
            if node.pk:
                queryset = queryset.exclude(pk=node.pk)
            try:
                right_sibling = queryset[:1][0]
            except IndexError:
                # No suitable right sibling could be found
                pass
        return right_sibling