Bubbling events in nested Backbone (Marionette) Models / Collections

Question

We have a large Marionette App, that uses Backbone.trackit to monitor unsaved changes in our Models.

We now have some nested models, in fact we have a Model, with a Collection of Models, that contain a Collection of Models.

trackit doesn't support the top level model being marked as 'dirty' when the child models change - due to backbone not bubbling these change events.

I know we could manually monitor these change events, but Im looking for a generic solution.

Has anyone had any experience of the following libs or any other solutions for this?

1. backbone-deep-model
2. Backbone Associations events
3. Custom Backbone.Model.set override that bubbles change events

The immediate requirement is to get trackit working with nested events - but I cant find any branches to trackit that add this.

So I was wondering if anyone has approached this, or used the above libs in conjunction with trackit?

Ideally, if a library would trigger a standard 'change' event all the way up the chain, then trackit would just pick up on this and start working.

so, if model.countries[3].regions[4].name changed, a change:countries event would be triggered on model. Thus if the model had trackit enbaled, it would all just work!

Answer 1

The events from models inside a collection already bubbles to the collection by default. So that's one thing solved and we just need to bubble events from a collection or another model inside a model.

One problem I see with bubbling events as-is up the hierarchy is that you then get false positive when you want to listen to that specific collection or model.

A way to avoid that is to namespace events that are bubbling up, but that may not work with trackit.

A simple implementation of a model that enables bubbling up events of arbitrary collections or other nested models:

var BubblingModel = Backbone.Model.extend({
    /**
     * Bubbles up any event triggered by 'object'.
     * @param {Backbone.Events} obj which implement the Backbone Events.
     * @param {String} key optional namespace name, default to 'nested'.
     */
    addNested: function(obj, key) {
        return this.listenTo(obj, 'all', function() {
            arguments[0] = (key || 'nested') + ':' + arguments[0];
            this.trigger.apply(this, arguments);
        });
    },
    removeNested: function(obj) {
        return this.stopListening(obj);
    }
});

and to use it:

var collection = new Backbone.Collection(),
    model = new BubblingModel();
model.addNested(collection, 'optional-key');

Any events from collection will be prefixed by its optional key or by the default nested string. A change:myAttribute event triggered by collection would be:

"optional-key:change:myAttribute"

Proof of concept with simple tests:

// The simple implementation
var BubblingModel = Backbone.Model.extend({
    /**
     * Bubbles up any event triggered by 'object'.
     * @param {Backbone.Events} obj which implement the Backbone Events.
     * @param {String} key optional namespace name, default to 'nested'.
     */
    addNested: function(obj, key) {
        return this.listenTo(obj, 'all', function() {
            arguments[0] = (key || 'nested') + ':' + arguments[0];
            this.trigger.apply(this, arguments);
        });
    },
    removeNested: function(obj) {
        return this.stopListening(obj);
    }
});

// Setting up a test with multiple nesting
var model5 = new Backbone.Model(),
    model4 = new Backbone.Model(),
    model3 = new BubblingModel({ model: model4 }),
    col2 = new Backbone.Collection([model3]),
    model2 = new BubblingModel({ col: col2 }),
    col1 = new Backbone.Collection([model2]),
    model1 = new BubblingModel({ col: col1 });

// Set which you want to bubble up.
model3.addNested(model4, 'model3-nested-model');
model2.addNested(col2, 'model2-nested-col')
    .addNested(model5);
model1.addNested(col1, 'model1-nested-col');

// listen from any model down the chain
Backbone.listenTo(model2, 'all', function(eventName) {
    console.log("model2:", eventName);
});
Backbone.listenTo(model1, 'all', function(eventName) {
    console.log("model1:", eventName);
});

// trigger default or custom events
model3.set('test', 1);
model3.trigger('model3');
model4.trigger('model4');
model5.trigger('model5');

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