Failed to implement computed property in emberjs - ember.js

Question

My fixture data contains multiple array.Out of this multiple array cart_items contains some product data.
I am trying to calculate total no of products available in cart data (based on length of cart_items items) but i am not able to calculate no of items are present in cart_items.
In router i have selected application fixture as model for current route,as follow :
Astcart.IndexRoute = Ember.Route.extend({
model: function() {
return Astcart.Application.find();
}
});
Computed property code :
Astcart.IndexController = Ember.ArrayController.extend({
tot_cart_prd: function() {
return this.get("model.cart_items").get('length');
}.property("#each.isLoaded")
});
And my fixture data is :
Astcart.Application.adapter = Ember.FixtureAdapter.create();
Astcart.Application.FIXTURES = [
{
"logo_url": "img/logo.jpg",
"logged_in": {
"logged": true,
"username": "sachin",
"account_id": "4214"
},
"category_list": [
{
"id": "1",
"name": "Mobiles & Accessories"
},
{
"id": "2",
"name": "Computers & Software"
},
{
"id": "3",
"name": "Fashion"
},
{
"id": "4",
"name": "Electronics"
},
{
"id": "5",
"name": "Watches & Jewelry"
},
{
"id": "6",
"name": "Health & Beauty"
},
{
"id": "7",
"name": "Games"
},
{
"id": "8",
"name": "Books & Entertainment"
},
{
"id": "9",
"name": "Gaming"
},
{
"id": "10",
"name": "Shoes & Bags"
}
],
"cart_items": [
{
"id": "1",
"name": "Samsung Galaxy Tab 2",
"qty": "1",
"price": "1245.12",
"subtotal": "7842.23"
},
{
"id": "2",
"name": "Samsung Galaxy Tab 2",
"qty": "1",
"price": "1245.12",
"subtotal": "7842.23"
},
{
"id": "3",
"name": "Samsung Galaxy Tab 2",
"qty": "1",
"price": "1245.12",
"subtotal": "7842.23"
}
]
}
];
I have posted my code here(JSFiddle).
Can any one tell me why this.get("model.cart_items") is returning null?

Answer 1

Because your IndexController receive an array of Astcart.Application, from the route. You need to iterate in each application and get the length of each category list .
Your computed property need to be the following:
Astcart.IndexController = Ember.ArrayController.extend({
tot_cart_prd: function() {
var result = this.get('model').map(function(application) {
return application.get('category_list.length');
});
return result;
}.property('model.#each.category_list.length')
});
Here's an updated fiddle http://jsfiddle.net/marciojunior/PZZym/

Answer 2

I just looked at this and your core issue has something to do with the relationship setup between Application and Cart_items. The reason that this.get("model.cart_items").get('length') is failing is that this.get("model.cart_items") returns null. If you can get your relationship working you should be on the right track. I don't know anything about EmberModel, so I can't be of much help there.