Why doesn't Ruby on Rails fields_for work?

Question

Ruby on Rails

There are 3 models: Products, Orders, Linking model
Product:

has_many :purchaseds, :dependent => :destroy
has_many :orders, :through => :purchaseds

order

has_many :purchaseds, :dependent => :destroy
has_many :products, through: :purchaseds
accepts_nested_attributes_for :purchaseds

Purchased

belongs_to :product
belongs_to :order

In the controller I write:

@order = Order.new()
@products.each do |p|
   @order.purchaseds.build({
        :product_id => p.id
   })
end

As a result, my form is empty!

= form_for(@order) do |f|
  - f.fields_for :purchaseds do |p|
     = debug p

= debug @order.purchaseds outputs an array of objects as expected.

Answer 1

Found an error

= form_for(@order) do |f|
  = f.fields_for :purchaseds do |p|
     = debug p