def METHOD_NAME(self):
    try:
        form = self._form()
        form_data = self._request.POST.items()
        _appstruct = form.validate(form_data)
        with self._request.dbsession.no_autoflush:
            for dict_ in _appstruct["themes"]:
                obj = form.schema["themes"].children[0].objectify(dict_)
                self._request.dbsession.merge(obj)
        self._request.dbsession.flush()
        return HTTPFound(self._request.route_url("layertree"))
    except ValidationFailure as e:
        # FIXME see https://github.com/Pylons/deform/pull/243
        self._populate_widgets(form.schema)
        return {
            "title": form.title,
            "form": e,
            "form_render_args": tuple(),
            "form_render_kwargs": {"request": self._request, "actions": []},
            "deform_dependencies": form.get_widget_resources(),
        }