<%= f.fields_for :invoice_line_items do |item_form| %>
<%= render "line_items/invoice_line_item_fields", f: item_form %>
<% end %>
<%= f.fields_for :invoice_line_items,
LineItem.new,
child_index: "NEW_RECORD" do |item_form| %>
<%= render "line_items/invoice_line_item_fields", f: item_form %>
<% end %>
<%= f.submit %>
<% end %>