rails 3, paperclip (& formtastic) - deleting image attachments

Question

I can't seem to find an example that is complete in all the components. I am having a hard time deleting image attachments

1. Classes

     class Product
       has_many :product_images, :dependent => :destroy
       accepts_nested_attributes_for :product_images
     end
   
     class ProductImage
       belongs_to :product
       has_attached_file :image #(etc)
     end
   

2. View

     <%= semantic_form_for [:admin, @product], :html => {:multipart => true} do |f| %>
       <%= f.inputs "Images" do %>
         <%= f.semantic_fields_for :product_images do |product_image| %>
           <% unless product_image.object.new_record? %>
             <%= product_image.input :_destroy, :as => :boolean, 
                :label => image_tag(product_image.object.image.url(:thumb)) %>
           <% else %>
             <%= product_image.input :image, :as => :file, :name => "Add Image" %>
           <% end %>
         <% end %>
       <% end %>
     <% end %>
   

3. Controller

     class Admin::ProductsController < AdminsController
      def edit
        @product = Product.find_by_permalink(params[:id])
        3.times {@product.product_images.build} # added this to create add slots
      end
   
      def update
         @product = Product.find_by_permalink(params[:id])
   
         if @product.update_attributes(params[:product])
           flash[:notice] = "Successfully updated product."
           redirect_to [:admin, @product]
         else
           flash[:error] = @product.errors.full_messages
           render :action => 'edit'
         end
       end
     end
   

Looks good, but, literally nothing happens when I check the checkbox. In the request I see:

      "product"=>{"manufacturer_id"=>"2", "size"=>"", "cost"=>"5995.0", 
         "product_images_attributes"=>{"0"=>{"id"=>"2", "_destroy"=>"1"}}

But nothing gets updated and the product image is not saved.

Am I missing something fundamental about how 'accepts_nested_attributes_for' works?

Answer 1

From the API docs for ActiveRecord::NestedAttributes::ClassMethods

:allow_destroy

If true, destroys any members from the attributes hash with a _destroy key and a value that evaluates to true (eg. 1, ‘1’, true, or ‘true’). This option is off by default.

So:

accepts_nested_attributes_for :product_images, allow_destroy: true