chats.js

Rooms = new Mongo.Collection('rooms');
Messages = new Mongo.Collection('messages');

if (Meteor.isClient) {
  Meteor.subscribe('rooms', function () {
    var room = Rooms.findOne();
    Meteor.subscribe('messages', room._id);
  });
}

if (Meteor.isServer) {
  Meteor.publish('rooms', function () {
    return Rooms.find();
  });

  Meteor.publish('messages', function (roomId) {
    var cursor = Rooms.find({_id: roomId});
    var self = this;

    var publishMessages = function (roomId) { 
      Messages.find({roomId: roomId})._publishCursor(self);
    };

    cursor.observeChanges({
      added: function (roomId, room) {
        if (room.isAccepted)
          publishMessages(roomId);
      },

      changed: function (roomId, room) {
        if (room.isAccepted) {
          publishMessages(roomId);
        }
      }
    });

    this.ready();
  });

  if (Rooms.find().count() == 0) {
    var roomId = Rooms.insert({name: 'My Room', isAccepted: false});
    Messages.remove({});
    Messages.insert({roomId: roomId, message: 'Hello'});
    Messages.insert({roomId: roomId, message: 'World'});
  }
}