How to use Ember-Data associations in conjunction with an ArrayProxy - ember.js

Question

I am trying to migrated my app to using Ember-Data as it's persistence mechanism. One thing that strikes me is that I'm not sure if it's still possible to use an arrayProxy for aggregate properties of a hasMany association. In my previous iteration I didn't have any explicit associations, just controllers tied together by specific properties. Now I'd like to take advantage of the association functionality in ember-data, but I am getting errors when I trie to bind the content of my array proxy to the "children" property of the DS.Model. My code is below and there is a jsfiddle here: http://jsfiddle.net/sohara/7p6gb/22/
The error I get is:
Uncaught TypeError: Object App.recipeController.content.ingredients has no method 'addArrayObserver'
I would like to be able to retain a controller layer, even if the data associations are controlleed at the model level. It'd also (ideally) like the child objects to be embedded in the json representation of the parent object in order to avoid multiple server requests.
window.App = Ember.Application.create();
App.store = DS.Store.create({
revision: 3,
adapter: DS.fixtureAdapter
});
App.Ingredient = DS.Model.extend({
name: DS.attr('string'),
price: DS.attr('string')
});
App.Recipe = DS.Model.extend({
name: DS.attr('string'),
ingredients: DS.hasMany('App.Ingredient', {embedded: true} )
});
App.Recipe.FIXTURES = [
{id: 1, name: 'Pizza', ingredients: [{id: 1, name: 'tomato sauce', price: 2, recipeId: 1}]}
];
App.recipeController = Ember.Object.create({
content: App.store.find(App.Recipe, 1)
});
App.ingredientsController = Ember.ArrayProxy.create({
content: 'App.recipeController.content.ingredients',
totalWeigth: function() {
var price = 0;
items = this.get('content');
items.forEach(function(item) {
weight += price;
});
}.property()
});

Answer 1

In App.ingredientsController you need to have contentBinding: 'App.recipeController.content.ingredients', instead of content: ...