def _move_child_within_tree(self, node, target, position):
        left = getattr(node, self.left_attr)
        right = getattr(node, self.right_attr)
        level = getattr(node, self.level_attr)
        width = right - left + 1
        tree_id = getattr(node, self.tree_id_attr)
        target_left = getattr(target, self.left_attr)
        target_right = getattr(target, self.right_attr)
        target_level = getattr(target, self.level_attr)

        if position == 'last-child' or position == 'first-child':
            if node == target:
                raise InvalidMove(_('A node may not be made a child of itself.'))
            elif left < target_left < right:
                raise InvalidMove(_('A node may not be made a child of any of its descendants.'))
            if position == 'last-child':
                if target_right > right:
                    new_left = target_right - width
                    new_right = target_right - 1
                else:
                    new_left = target_right
                    new_right = target_right + width - 1
            else:
                if target_left > left:
                    new_left = target_left - width + 1
                    new_right = target_left
                else:
                    new_left = target_left + 1
                    new_right = target_left + width
            level_change = level - target_level - 1
            parent = target
        elif position == 'left' or position == 'right':
            if node == target:
                raise InvalidMove(_('A node may not be made a sibling of itself.'))
            elif left < target_left < right:
                raise InvalidMove(_('A node may not be made a sibling of any of its descendants.'))
            if position == 'left':
                if target_left > left:
                    new_left = target_left - width
                    new_right = target_left - 1
                else:
                    new_left = target_left
                    new_right = target_left + width - 1
            else:
                if target_right > right:
                    new_left = target_right - width + 1
                    new_right = target_right
                else:
                    new_left = target_right + 1
                    new_right = target_right + width
            level_change = level - target_level
            parent = getattr(target, self.parent_attr)
        else:
            raise ValueError(_('An invalid position was given: %s.') % position)

        left_boundary = min(left, new_left)
        right_boundary = max(right, new_right)
        left_right_change = new_left - left
        gap_size = width
        if left_right_change > 0:
            gap_size = -gap_size

        opts = self.model._meta
        # The level update must come before the left update to keep
        # MySQL happy - left seems to refer to the updated value
        # immediately after its update has been specified in the query
        # with MySQL, but not with SQLite or Postgres.
        move_subtree_query = """
        UPDATE %(table)s
        SET %(level)s = CASE
                WHEN %(left)s >= %%s AND %(left)s <= %%s
                  THEN %(level)s - %%s
                ELSE %(level)s END,
            %(left)s = CASE
                WHEN %(left)s >= %%s AND %(left)s <= %%s
                  THEN %(left)s + %%s
                WHEN %(left)s >= %%s AND %(left)s <= %%s
                  THEN %(left)s + %%s
                ELSE %(left)s END,
            %(right)s = CASE
                WHEN %(right)s >= %%s AND %(right)s <= %%s
                  THEN %(right)s + %%s
                WHEN %(right)s >= %%s AND %(right)s <= %%s
                  THEN %(right)s + %%s
                ELSE %(right)s END,
            %(parent)s = CASE
                WHEN %(pk)s = %%s
                  THEN %%s
                ELSE %(parent)s END
        WHERE %(tree_id)s = %%s""" % {
            'table': qn(opts.db_table),
            'level': qn(opts.get_field(self.level_attr).column),
            'left': qn(opts.get_field(self.left_attr).column),
            'right': qn(opts.get_field(self.right_attr).column),
            'parent': qn(opts.get_field(self.parent_attr).column),
            'pk': qn(opts.pk.column),
            'tree_id': qn(opts.get_field(self.tree_id_attr).column),
        }

        cursor = connection.cursor()
        cursor.execute(move_subtree_query, [
            left, right, level_change,
            left, right, left_right_change,
            left_boundary, right_boundary, gap_size,
            left, right, left_right_change,
            left_boundary, right_boundary, gap_size,
            node.pk, parent.pk,
            tree_id])

        # Update the node to be consistent with the updated
        # tree in the database.
        setattr(node, self.left_attr, new_left)
        setattr(node, self.right_attr, new_right)
        setattr(node, self.level_attr, level - level_change)
        setattr(node, self.parent_attr, parent)
Yield :class:`.Completion` instances.
dataset/ETHPy150Open agiliq/django-socialnews/socialnews/mptt/managers.py/TreeManager._move_child_within_tree--crossover with--dataset/ETHPy150Open jonathanslenders/python-prompt-toolkit/prompt_toolkit/completion.py/Completer.get_completions