Rails Paperclip inserting instead of updating - ruby-on-rails

Question

I created a simple application that has a Product and an Image model. Product has_many Images and Images has an attached file attribute (paperclip).
I created a simple_form for creating/editing Products and it works fine on creation. However, when editing a Product that has N images, rails inserts more N files - empty files.
I have set up a Simple Form custom input that tests if the image attachment exists in which case instead of rendering the builders input, it only renders an image_tag().
I see the html generated and it show something strange, a hidden tag:
<input id="product_images_attributes_0_id" name="product[images_attributes][0][id]" type="hidden" value="14">
And in the rails server console I see:
Processing by ProductsController#update as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"asdfasdfaasdf=", "product"=>{"reference"=>"Y1112CYL.E2", "images_attributes"=>{"0"=>{"id"=>"14"}}}, "commit"=>"Update Product", "id"=>"20"}
Product Load (0.6ms) SELECT "products".* FROM "products" WHERE "products"."id" = $1 LIMIT 1 [["id", "20"]]
Unpermitted parameters: id
(0.2ms) BEGIN
SQL (1.0ms) INSERT INTO "images" ("created_at", "imageable_id", "imageable_type", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id" [["created_at", Tue, 18 Feb 2014 05:05:13 UTC +00:00], ["imageable_id", 20], ["imageable_type", "Product"], ["updated_at", Tue, 18 Feb 2014 05:05:13 UTC +00:00]]
(0.6ms) COMMIT
Here is the code to my implementation. If someone could help I would be very happy! Please pardon me if I left out any import part of the code, I will gladly edit the question to include it.
_form.html.erb
<%= simple_form_for(#product) do |f| %>
<%= f.error_notification %>
<div class="inputs">
<%= f.input :reference %>
<h3>Images</h3>
<div id='images'>
<%= f.simple_fields_for :images do |image| %>
<%= render 'image_fields', :f => image %>
<% end %>
<div class='links'>
<%= link_to_add_association 'New image', f, :images %>
</div>
</div>
</div>
<div class="actions">
<%= f.button :submit %>
</div>
<%end%>
_image_fields.html.erb
<%= content_tag :div, class: "nested-fields images-fields" do %>
<%= content_tag :div, id: "new-image" do %>
<% if f.object.photo.exists? %>
<% f.template.image_tag(f.object.photo.url(:thumb)) %>
<% else %>
<% f.input :photo, :as => :photo %>
<% end %>
<% end %>
<% end %>
app/inputs/photo_input.erb
class PhotoInput < SimpleForm::Inputs::FileInput
def input
out = '' # the output string we're going to build
# check if there's an uploaded file (eg: edit mode or form not saved)
if object.send("#{attribute_name}?")
# append preview image to output
# <%= image_tag #user.avatar.url(:thumb), :class => 'thumbnail', id: 'avatar' %>
out << template.image_tag(object.send(attribute_name).url(:thumb), :class => 'thumbnail', id: 'photo')
else
# append file input. it will work accordingly with your simple_form wrappers
(out << #builder.file_field(attribute_name, input_html_options)).html_safe
end
end
end
ProductsController#update
def update
respond_to do |format|
if #product.update(product_params)
format.html { redirect_to #product, notice: 'Product was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #product.errors, status: :unprocessable_entity }
end
end
end

Answer 1

For posterity, #omarvelous' comment seems to have solved it:
I added the reject if all blank to my accepts_nested_attributes_for
accepts_nested_attributes_for :images, :allow_destroy => true, :reject_if => :all_blank
Edit:
It turns out there is an issue with this solution. When reject_if => :all_blank is it stops the destroy from working properly. See this post that shows a workaround -- that I did not manage to get to work.