form.fields_for do for a finite number of times

I have two models, Product and ProductImage, and I'd like to offer the possibility to add up to 6 images to each product.

Product

has_many :product_images, :dependent => :destroy

while ProductImage

belongs_to :product

So far, my views are the following:

#products/_form.html.erb.
    <% @product.product_images.build %>
    <%= form_for(@product, :html => { :multipart => true }) do |product_form| %>
      <% if @product.errors.any? %>
        <div id="error_explanation">
          <h2><%= pluralize(@product.errors.count, "error") %> prohibited this product from being saved:</h2>

          <ul>
          <% @product.errors.full_messages.each do |msg| %>
            <li><%= msg %></li>
          <% end %>
          </ul>
        </div>
      <% end %>

      <div class="field">
        <%= product_form.label :title %><br />
        <%= product_form.text_field :title %>
      </div>
      <div class="field">
        <%= product_form.label :description %><br />
        <%= product_form.text_area :description %>
      </div>
      <div class="field">
        <%= product_form.label :price %><br />
        <%= product_form.text_field :price %>
      </div>
      <div id="product_images">
          <%= render :partial => 'product_images/form', :locals => {:form => product_form} %> 
        </div>
      <div class="actions">
        <%= product_form.submit %>
      </div>
    <% end %>

and

#product_images/_form.html.erb
    <%= form.fields_for :product_images do |product_image_form| %>
        <div class="image">
            <%= product_image_form.label :image, 'Image:' %>
            <%= product_image_form.file_field :image %>
        </div>
        <% unless product_image_form.object.nil? || product_image_form.object.new_record? %>
        <div class="image">
            <%= product_image_form.label :_destroy, 'Remove:' %>
            <%= product_image_form.check_box :_destroy %>
        </div>
        <% end %>
    <% end %> 

The question is: how do I force my partial form to print out 6 different file_fields, each with its own unique attribute name, e.g.:

name="product[product_images_attributes][0][image]"
name="product[product_images_attributes][1][image]"

and so on?

I mean, is tha开发者_如何学Pythont even possible or there is a better and different way to achieve such result?

I was thinking I could add as many fields with link_to and AJAX but I guess it's a lot easier for the user to have the six fields printed out and ready, instead of clicking a link each time in order to add a field.

Assuming you use accepts_nested_attributes_for :product_images in your Product model, you need something like the following in your ProdcutsController:

def new
  @product = Product.new
  6.times { @product.product_images.build } # this will create 6 "blank product_images"
end

def edit
  @product = Product.find(params[:id]).includes(:product_images)
  (6 - @product.product_images.size).times { @product.product_images.build } # this will create as many "blanks" as needed
end

For new products, you build 6 new product images, for existing products you build only as many as you need in order to have 6.

Edit: Also remove the <% @product.product_images.build %> line from your products/_form.html.erb view since you are building the associated instances in your controller instead.