How to 'transform' data returned via a Meteor.publish?

Question

Meteor Collections have a transform ability that allows behavior to be attached to the objects returned from mongo.

We want to have autopublish turned off so the client does not have access to the database collections, but we still want the transform functionality.

We are sending data to the client with a more explicit Meteor.publish/Meteor.subscribe or the RPC mechanism ( Meteor.call()/Meteor.methods() )

How can we have the Meteor client automatically apply a transform like it will when retrieving data directly with the Meteor.Collection methods?

Answer 1

While you can't directly use transforms, there is a way to transform the result of a database query before publishing it. This is what the "publish the current size of a collection" example describes here.

It took me a while to figure out a really simple application of that, so maybe my code will help you, too:

Meteor.publish("publicationsWithHTML", function (data) {
    var self = this;
    Publications
        .find()
        .forEach(function(entry) {
            addSomeHTML(entry);  // this function changes the content of entry
            self.added("publications", entry._id, entry);
        });
    self.ready();
});

On the client you subscribe to this:

Meteor.subscribe("publicationsWithHTML");

But your model still need to create a collection (on both sides) that is called 'publications':

Publications = new Meteor.Collection('publications');

Mind you, this is not a very good example, as it doesn't maintain the reactivity. But I found the count example a bit confusing at first, so maybe you'll find it helpful.

Answer 2

Try:

let transformTodo = (fields) => {
  fields._pubType = 'todos';
  return fields;
};

Meteor.publish('todos', function() {
  let subHandle = Todos
    .find()
    .observeChanges({
      added: (id, fields) => {
        fields = transformTodo(fields);
        this.added('todos', id, fields);
      },
      changed: (id, fields) => {
        fields = transformTodo(fields);
        this.changed('todos', id, fields);
      },
      removed: (id) => {
        this.removed('todos', id);
      }
    });
  this.ready();
  this.onStop(() => {
    subHandle.stop();
  });
});