def on_order
      supply = find_or_create_supply_detail
      composite = supply.stock.first
      if composite.nil?
        composite = ONIX::Stock.new
        supply.stock << composite
      end
      composite.on_order
    end
def on_order
      supply = find_or_create_supply_detail
      composite = supply.stock.first
      if composite.nil?
        composite = ONIX::Stock.new
        supply.stock << composite
      end
      composite.on_order
    end
retrieve the number on order