simple_fields_for not showing up [rails 4]

问题

Im trying to create two hidden fields, and one shows up no problem, but the other that comes from the nested form does not

product.rb

class Product < ActiveRecord::Base
  has_many :product_options,  dependent: :destroy
  accepts_nested_attributes_for :product_options, allow_destroy: true, :reject_if => proc { |x| x[:option_name].blank? }
  belongs_to :user
end 

product_option.rb

class ProductOption < ActiveRecord::Base
  belongs_to :product
end

products_controller.rb

class ProductsController < ActionController::Base
  layout "application"

  def index 
    @products = Product.all
    @current_user = Client.find_by(id: session[:client])
    if @current_user.redeemed == true 
      redirect_to root_path
    end
  end 

  def show
    @product = Product.find(params[:id])
    @product_option = @product.product_options.find(params[:id])
    @current_user = Client.find_by(id: session[:client])
    @current_user.update(:product_option => @product_option.option_name)
    @current_user.update(:selected_product => @product.id)
    render :nothing => true
  end

  private
    def product_params
      params.require(:product).permit(:name, :id, :position, :product_description, :product_image_type, :product_image, :product_detail, :product_option_id, 
          :product_options_attributes => [:id, :option_name, :ranking, :total_redeemed, :product_id])
    end
end

_form.html.erb

<%= simple_form_for Product.new, :method => "post",:remote => true, :class => "item_prompt" do |f| %> 
      <%= f.hidden_field :id, :class => 'product_id' %>
        <%= f.simple_fields_for :product_options do |ff| %>
          <%= ff.hidden_field :id, :class => 'product_option_id' %>
        <% end %>
      <%= f.submit "Yep!", :class => "yep ready_button confirm_button", :name => "confirm_button" %>
    <% end %>

html output

<form accept-charset="UTF-8" action="/products" class="simple_form new_product" data-remote="true" id="new_product" method="post" novalidate="novalidate">
  <input class="product_id" id="product_id" name="id" type="hidden" value="240">
  <input class="yep ready_button confirm_button" name="confirm_button" type="submit" value="Yep!">
<form>

回答1:

I figured this out, ... the problem was

fields_for will loop over a collection association, rendering out as many times as there are items in it, which means 0 times if the association is empty

so to fix the problem I had to add

@product = Product.new
@product.product_options.build

to the index action in the controller.

来源：https://stackoverflow.com/questions/26788432/simple-fields-for-not-showing-up-rails-4