Is it possible to initialise a backbone Collection with object IDs rather than objects?

Question

I have a Backbone.js Collection and I have an array of model IDs that I want to populate it. I know that I could fetch these objects one by one, build an array of objects and pass them into the Collection's constructor as an array.

What I'd like to be able to do is pass the array of object ids into the constructor as initial data, and get the Collection to fetch them, possibly as batch, as per this.

Doable?

Answer 1

When you call 'fetch' on a Backbone.Collection, it in turn calls Backbone.sync, which by default just asks the collection for the url to use.

So if your server responds to:

/models/batch/?ids=1,2,3,4

You could do something like:

var MyCollection = Backbone.Collection.extend({

    model: Model,

    url: '/models',

    initialize: function(models, options) {
        ids = options.ids || [];
        if (ids.length > 0) { 
            this.fetchByIds(ids);
        }
    },

    fetchByIds: function(ids) {
        // Save a reference to the existing url
        var baseUrl = this.url;

        // Assign our batch url to the 'url' property and call the server
        this.url += '/?ids=' + ids.join(',');
        this.fetch();

        // Restore the 'url' property
        this.url = baseUrl;
    }
});

And use it like so:

var coll = new MyCollection({}, {ids: [1, 2, 3, 4]});

You'd have to pass the ids in the options parameter, because the Backbone.Collection constructor function sets the models passed in the first parameter before it calls the 'initialize' function.

Theoretically, this should work (read: completely untried).