nested form returns empty hash in params

Question

Hi this is strange I have 3 models

class Deal < ActiveRecord::Base
  has_many :deal_items, :dependent => :destroy
  accepts_nested_attributes_for :deal_items 
  attr_accessible :deal_items_attributes

end
class DealItem < ActiveRecord::Base
  self.table_name = "deals_menu_items"
  has_many :swap_items, :dependent => :destroy
  belongs_to :deal
  has_many :deal_menu_prices

  has_many :menu_items, through: :deal_menu_prices
  belongs_to :item_price

  accepts_nested_attributes_for :deal_menu_prices
  attr_accessible :deal_menu_prices_attributes
end

and

class DealMenuPrice < ActiveRecord::Base
  belongs_to :menu_item
  belongs_to :deal_item
  belongs_to :item_price
  attr_accessible :item_price_id, :deal_item_id, :menu_item_id, :included
end

and i have view template

<%= nested_form_for @deal do |f| %>
  <%= f.fields_for :deal_items do |d| %>
    <%= d.fields_for :deal_menu_prices do |dm| %>
       <%= dm.select :item_price_id, :options_for_select(my_options) %>
    <% end %>
  <% end %>
<% end %> #deal form end

but in my controller i get every thing empty e.g

"deal"=>{"deal_items_attributes"=>{"0"=>{}}, "user_id"=>4}

what i am doing wrong and there is no deal_menu_prices_attributes in deal_items_attributes hash. I am expecting something like this

"deal"=>{"deal_items_attributes"=>{"0"=>{"deal_menu_prices_attributes"=>{item_price_id: 1} }}, "user_id"=>4}