3 models in a form.

Hello,

class Customer < ActiveRecord::Base has_many :deliveries

class Delivery < ActiveRecord::Base has_many :delivery_items has_many :products, :through => :delivery_items belongs_to :customer

class DeliveryItem < ActiveRecord::Base belongs_to :delivery belongs_to :product

I create a new delivery for customer x:

= simple_form_for @customer do |f| = f.simple_fields_for :deliveries do |deliveries_f|    .block      .column.span-12        = deliveries_f.association :products, :multiple => true, :selected => @products_selected_id,                                   :input_html => { :title => "- Select product -" }, :label => false        = deliveries_f.input :notes

DeliveryItem has the extra attribute quantity. In this form I have to set a quantity DeliveryItem attribute so that I create a Delivery for customer x, associate one or more Product and for a product set the quantity. How can I do in the form?

Any advice?