var reg_handler = function (act) {
  UserModel.update({ $or: [{nick: act.nick}, {hmask: act.host}] }, { $set: { lastfm: act.params } }, { upsert: true }, function(){});
};

这正是我想要的，而且它是一行。 ：D完美！

This does exactly what I wanted, and it's one line. :D Perfect!