for m in users_group.members:

            u = m.user

            if u.user_id == user.user_id:

                return m

        try:

            users_group_member = UsersGroupMember()

            users_group_member.user = user

            users_group_member.users_group = users_group

            users_group.members.append(users_group_member)

            user.group_member.append(users_group_member)

            self.sa.add(users_group_member)

            return users_group_member

        except:

            log.error(traceback.format_exc())

            raise

    def has_perm(self, users_group, perm):

        if not isinstance(perm, Permission):

            raise Exception('perm needs to be an instance of Permission class')

        users_group = self.__get_users_group(users_group)

        return UsersGroupToPerm.query()\

            .filter(UsersGroupToPerm.users_group == users_group)\

            .filter(UsersGroupToPerm.permission == perm).scalar() is not None

    def grant_perm(self, users_group, perm):

        if not isinstance(perm, Permission):

            raise Exception('perm needs to be an instance of Permission class')

        users_group = self.__get_users_group(users_group)

        new = UsersGroupToPerm()

        new.users_group = users_group

        new.permission = perm

        self.sa.add(new)

    def revoke_perm(self, users_group, perm):

        if not isinstance(perm, Permission):

            raise Exception('perm needs to be an instance of Permission class')

        users_group = self.__get_users_group(users_group)

        obj = UsersGroupToPerm.query()\

            .filter(UsersGroupToPerm.users_group == users_group)\

        self.sa.delete(obj)