Nested form

gistfile1.rb

<%  @product.images.build if @product.images.blank? %>
<%= f.simple_fields_for :images do |img| %>
  <% unless @product.images.first.file.blank? %>
      <div class="control-group">
         <label class="controls"><%= image_tag @product.images.first.file %></label>
      </div>   
      <%= img.input :_destroy, :label => "Remove", :as => :boolean %>
  <% end %>
      <%= img.input :file, :as => :file, :label => "Picture", input_html: { class: "input-hundredpercent" } %>
<% end %>