hierarchy.py

    (...)
  
    tabs = dbsession.query(
        Folder
    ).join(
        root, root.c.id == Folder.id
    ).add_columns(
        root.c.level.label('level')
    ).order_by(
        root.c.container_id, root.c.level.desc(), root.c.weight.desc()
    ).all()

    per_level = itertools.groupby(reversed(tabs), lambda x: x.level)

    def _merge(a, b):
        if not b:
            b.extend(a)
        else:
            while a:
                a_ = a.pop()
                visited = []

                for b_ in b:
                    if a_['folder'] is b_['folder'].parent:
                        a_['children'].append(b_)
                        visited.append(b_)

                for v in visited:
                    b.remove(v)

                b.append(a_)


    sorted_tabs = []
    for level, level_tabs in per_level:
        level_tabs = [{'folder': f.Folder, 'children': []} for f in level_tabs]
        _merge(level_tabs, sorted_tabs)

    return sorted_tabs