% i = 0 %>
<%= f.hidden_field :page_id, value: @page_id %>
<%= f.fields_for :sub_parts do |sub| %>
Module :
<%= sub.select(:module, @modules,{:include_blank => true}, "data-number"=> "pp_#{i}", "class" => "module_name") %>
<%= sub.label(:widget,@part.sub_parts[i].widget) rescue nil %>
<%= sub.hidden_field(:widget) if i < @part.sub_parts.count %>
<% i = i + 1 %>
<% end %>
<%= f.submit %>