gistfile1.txt

  belongs_to :order
  belongs_to :item

  validate :item_has_not_been_sent?

  def user
    self.order.user
  end

  def item_has_not_been_sent?
    matching_order_items = user.order_items.where(:item_id => self.item_id).where(:size => self.size)
    matching_order_items = matching_order_items.where{id != self.id} unless new_record?
    
    if matching_order_items.exists?
      errors.add(:item_id, "This item has already been sent to this user")
    end
  end