# I have an order
class Order < ActiveRecord::Base
  has_many :order_items
end
# with items
class OrderItem < ActiveRecord::Base
  belongs_to :family
  belongs_to :order
  has_many :order_items

# I sort the order items via a scope which joins with item family to sort them accordingly
  scope :default_order, joins(:family).order('families.name, order_items.quantity')
end

# Controller
def edit
   @order = Order.find params[:id]
   @ois = @order.order_items.default_order
end

# My problem is in the update method, if we have errors and must show the order to the user...
#    How do I sort my items?
def update
    ...
    if @order.update_attributes(params[:order])
       ...
    else #it doesn't validate
       #if I do
       @ois = @order.order_items.default_order
      # items are reloaded (with the correct order) BUT user input and validation errors are lost.
      # how do I keep the sorting + data?!?
    end
end