Question

In the context of a Collection, I want to retrive a model instance based on some object containing model data, but I don’t want to hard code the idAttribute.

Backbone makes things easy when you already have a model instance, you can just access its .id property and it sorts things out, but I can’t seem to find a way of going the other way, short of creating a instance of a model just to get at its idAttribute.

For example:

var Cat = Backbone.Model.extend({
  defaults: {
    name: '',
    age: null
  },

  idAttribute: 'name'
});

var PushCollection = Backbone.Collection.extend({
  initialize: function () {
    coll = this;
    somePushConnection.on('deleted', function (deleted) {
      _.each(deleted, function (obj) {
        // obj being something like: {name: 'mittens', age: 302}
        var model = coll.get(obj[coll.model.idAttribute]); // Can't do this!
        if (model) { model.destroy(); }
      });
    });
  }
});

var Cats = PushCollection.extend({
  model: Cat
});

Answer 1

You should be able to access it via the model’s prototype:

Model.prototype.idAttribute

Or in your sample code

var model = coll.get(obj[coll.model.prototype.idAttribute]);