foo.py

    @view_config(request_method='GET', renderer='string',
                 name='hierarchy', accept='application/json')
    def hierarchy(self):
        from amnesia.modules.folder import Folder
        from amnesia.modules.folder.services import get_children
        from amnesia.modules.folder.validation import FolderSchema
        from pyramid.renderers import JSON
        from pyramid.response import Response

        schema = FolderSchema(only=('id', 'title'))
        json = JSON()
        json.add_adapter(Folder, lambda obj, req: schema.dump(obj))

        result = get_children(
            self.request.dbsession,
            self.context.entity.id
        )

        return json(result)