Chaining expressions after .changes() has been called

[rclai]

I was made aware that after you've called .changes(), you can actually .map(), and even .filter() the changes that come in like this: .changes().filter(...). I posted an issue asking why .get().pluck() wouldn't work and they told me that a workaround would involve having to chain expressions after .changes() to get the functionality you want. This seems to be a common thing to do to work around the limitations of change-feeds.

var fields = r.expr([ 'id', 'b', 'c' ]);
r.table('cities').get(...).changes().filter(function (row) {
  return fields.contains(function (field) {
    // compare the fields we care about
    return row('new_val')(field).ne(row('old_val')(field)).default(true);
  })
});

In terms of publishing a change-feed in Meteor in a simple way, it seems like doing something like the above is going to be tough to pull-off, to make it simple in a .publish(), that is. So if you really wanted to publish something like the above, you would need to write a change-feed manually, like:

Meteor.publish('city', function (id) {
  var self = this;
  var init = true;
  var stream = Cities.get(id).changes().filter(function (row) {
    return fields.contains(function (field) {
      return row('new_val')(field).ne(row('old_val')(field)).default(true);
    })
  }).run().each(function (err, notif) {
    if (err) {
      self.error(err);
    } else if (init) {
      init = false;
      self.added(Cities.name, /* the initial value */)
      self.ready();
    } else {
      // A bunch of logic to do
      // self.added, self.changed and self.removed
    }
  });

  self.onStop(function () {
    stream && stream.close();
  });
});

I wrote this to hopefully discuss how we can make this simpler, since that's what Meteor strives to be.