Listen to a specific attribute changes in a model in a nested collection in Backbone

Question

I have the following backbone structure:

- collection[order_items]
   - collection[menu_items]
        - price
        - quantity

and I want to listen for any changes in the quantity attribute, I got it working by

var CheckoutView = Backbone.Marionette.ItemView.extend({

    template: '#template-checkout',

    initialize: function (options) {
        this.order_collection = options.collection;
        _(this.order_collection.models).each(function (element, index, list) {
            this.listenTo(element.get("menu_items"), "change:quantity", this.onOrderItemsChanged);
        }, this);

    },

    onOrderItemsChanged: function (model, val, options) {
        console.log(model.get("name"));
    }

});

But does marionette or backbone have a better way of doing it, instead of looping throught the parent collection and adding the listener to each child collection, maybe something like

this.listenTo(this.order_collection, "change:menu_items:quantity", this.on OrderItemsChanged)

(which didnt work for me)

score 6 · Accepted Answer · answered Apr 28 '13 at 07:10

Take a look at Backbone.DeepModel. Apparently, you can represent Order as a single model with deep structure and listen to either change:order_items.*.menu_items.* or change:order_items.menu_items.*. Note that this solution prevents you from using benefits of nested lists as Backbone.Collection. I think it's a good tradeoff, but your mileage may vary

score -8 · Answer 2 · answered Apr 28 '13 at 13:56

-8

Backbone collection has its own events as Backbone models do. You just have to bind the event in your collection and all the models inside it will listen for it. Eg:

this.order_collection.models.on('change:quantity', function(model, updatedQuantity) {
    alert("Changed quantity from " + model.previous("quantity") + " to " + updatedQuantity););
});

So, events triggered on a model in a collection will also be triggered on the collection.

answered Apr 28 '13 at 13:56

ricardohdz

579
4
9

8

Sorry, I don't see how this works. `Collection.models` is a raw Array, and Array doesn't have an `on` method. Am I missing something? – ericsoco Jul 18 '13 at 06:44
@ericosoco is right, this doesn't work and I don't see how it could work. – dvdplm Aug 09 '13 at 06:58
2

Agreed - I think this should be updated to be "this.order_collection.on" rather than .models.on. – Bryan Rayner Oct 30 '13 at 00:04

Listen to a specific attribute changes in a model in a nested collection in Backbone

2 Answers2