def grp_by(self, name):
        """
        :returns: a dictionary grp_id -> TRT string
        """
        dic = {}
        for smodel in self.source_models:
            for src_group in smodel.src_groups:
                dic[src_group.id] = getattr(src_group, name)
        return dic
:returns: a dictionary grp_id -> TRT string