## views/orders/_form.html.erb

<%= f.error_messages %>

<div id="order_line_items">
  <%= render :partial => 'line_items', :locals => {:f => f, :order => @order} %>
</div>

## views/orders/_line_items.html.erb

<% f.fields_for :line_items do |line_items_forms| %>
  <tr>
    <td><%= line_items_forms.text_field :quantity, :size => 5 %></td>
    <td><%= line_items_forms.text_field :description, :size => 30 %></td>
    <td><%= line_items_forms.select :color_id, @colors.map {|c| [c.name, c.id]} %></td>
    <td><%= line_items_forms.text_field :price_per, :size => 10, :onblur => order.new_record? ?
      'updateExtendedPrice("order_line_items_attributes_0_quantity", this.id,
      "order_line_items_attributes_0_price_extended");' :
      "updateExtendedPrice('order_line_items_attributes_#{self.id.to_s.split('_')[5]}_quantity', this.id,
      'order_line_items_attributes_#{self.id.to_s.split('_')[5]}_price_extended');" %></td>
    <td><%= line_items_forms.text_field :price_extended, :size => 10, :class => 'fluffy_bunny' %></td>
  </tr>
<% end %>