If backend use `group` sql postgresql, how to express in frontend by ember data?

My backend use Rails and postgresql, and I have two model like:

class Order < ActiveRecord::Base
  has_many :products

  ...
  def arrange_products
    self.products.select("name, SUM(amount) as sum_amount").group("name").having("SUM(amount) != ?", 0)
  end
  ...
end

class Product < ActiveRecord::Base
  belongs_to :order
  ...
end

The arrange_products like has_many, but there are no id.

So in ember data use hasMany could not work.

Now I set attr for arrange_products in Order model:

export default Model.extend({
  products: hasMany('product'),
  ...
  arrange_products: attr('')
}); 

But I think it is not best way solve thie problem. So there is a good solution to this situation? Thanks.