<%= f_form_for [@user, @order] do |f| %>
<%= f.error_messages %>
<%= f.fields_for :order_items do |op_field| %>
<%= render op_field.object, f: op_field, product: op_field.object.product %>
<% end %>
<%= render 'order_items/total_price', f: f %>
<% end %>