RoleModel.js

/*
 * So, your json from here http://screencast.com/t/zv8sQGVk6 is organized like this:
 * array (roles) -> model (role) -> array (permissions) -> model (permission). Collections
 * already handle array -> model by design.  What you need to add is a model that contains a
 * collection; in other words, the role model should contain a permission collection.
 * That's what this file is :)
 */
var RoleModel = Backbone.Model.extend({

  // See http://backbonejs.org/#Model-parse
  // See backbone.js source code for Model.parse()--it's a simple return
  parse: function (response, options) {

    // 'response' is the literal json object from fetch() or sync() operations.
    // We need to replace the nested permissions json array with an actual collection.
    if (response.permissions) {
      response.permissions = new PermissionCollection(response.permissions);
    }

    return response;
  },

  // See http://backbonejs.org/#Model-toJSON
  // See backbone.js source code for Model.toJSON()--it's a simple shallow clone
  toJSON: function () {
    // Shallow clone of attributes--taken from backbone.js source for toJSON()
    var attributes = _.clone(this.attributes);

    // Since parse() turned permissions into a collection, we need to turn it back into JSON here.
    // The clone is ideal so that someone holding the toJSON result can't accidentally change the
    // contents of the collection.
    // See http://backbonejs.org/#Collection-models
    // See http://stackoverflow.com/a/21003060/957813
    attributes.permissions = _.map(attributes.permissions.models, _.clone);

    return attributes;
  }
});