How to build children of a nested form in the controller

I know how to build the 2nd object in a controller but how do you build a third or a fourth?

In my case i need to build 3.

Location - has_many :product_dates, :products
ProductDate - has_many :products & belongs_to :location
Product - belongs_to :location, :product_date

I build the Location and Product Date easily:

def new
  @location = Location.new
  @location.product_dates.build
end

Now i need to build the products on the form. Can anyone show me how to do this?

EDIT: Complete Answer:

def new
    @location = Location.new
    product_date = @location.product_dates.build
    product_date.products.build
end

    <%= form_for @location do |f| %>
    <%= f.text_field :business %>
    <%= f.t开发者_开发百科ext_field :address %>

    <%= f.fields_for :product_dates do |date| %>
    <%= date.date_select :date %>

    <%= date.fields_for :products do |product| %>
    <%= product.text_field :name %>
     <%= product.text_field :price %>
    <%= product.text_field :tag_list %>
    <% end %>
    <% end %>
    <%= f.submit "Create" %>        
<% end %>

---

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EDIT:

change the nested part with:

<%= f.fields_for :product_dates do |date| %>
  <%= date.date_select :date %>
  <%= date.fields_for :products do |product| %>
   <%= product.text_field :name %>
   <%= product.text_field :price %>
   <%= product.text_field :tag_list %>
  <% end %>
<% end %>

Because products are nested inside product_dates

---

add to your controller:

def new
  @location = Location.new
  @product_dates = @location.product_dates.build
  @product = @product_dates.product.build
end

in you ProductDate model:

class ProductDate < ActiveRecord::Base
  accepts_nested_attributes_for :products
...

in you Location model:

class Location < ActiveRecord::Base
  accepts_nested_attributes_for :product_dates
...

And you form should be like this:

<% f.fields_for :product_dates do |date| %>
  <%= date.text_field :content %>
  <% date.fields_for :products do |product| %>
    <%= product.text_field :content %>
  <%end %>
<% end %>