def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def _swdb_environment_upgrade(self, env_id, pkg_types, groups):
        if not self._base.history.env.get(env_id):
            self._raise_or_warn(self._ignore_installed,_("Environment id '%s' is not installed.") % env_id)
            return

        swdb_env = self._create_swdb_environment(env_id, pkg_types, groups)

        if swdb_env is not None:
            self._base.history.env.upgrade(swdb_env)