Meteor Collection Transform: is it done on the server or on the client? or it depends

javascript, meteor

Solution

UPDATE: It's possible to do a transform on the server.

You can have a transform on the client like this:

return YourCollection.find({}, {transform: function (doc) {
   doc.test = true;
   return true;
}});

Meteor ignores `transform` on queries that are published (from within `Meteor.publish`). The client sees the document as if the transform didn't exist.

If you would like to use transforms on the server you can do this:

YourCollection = new Mongo.Collection("collection_name"); 

Meteor.publish("yourRecordSet", function() {

  //Transform function
  var transform = function(doc) {
    doc.date = new Date();
    return doc;
  }

  var self = this;

  var observer = YourCollection.find().observe({
      added: function (document) {
      self.added('collection_name', document._id, transform(document));
    },
    changed: function (newDocument, oldDocument) {
      self.changed('collection_name', newDocument._id, transform(newDocument));
    },
    removed: function (oldDocument) {
      self.removed('collection_name', oldDocument._id);
    }
  });

  self.onStop(function () {
    observer.stop();
  });

  self.ready();

});

Problem

I want to use transform to make a "virtual field" out of a collection. However, the new field I'm adding (within the transform function) is adding quite a bit of data to the returned document. This is fine if the transform is taking place inside the client. If it is done on server-side, then there will be bandwidth concerns. So I'm wondering if the transform is done on the server, or on the client, or it depends on how I find/fetch the document?

Original source