Sexy methods for AR objects.

examples.rb

def unread_comments
  readable_comments.delete_if {|c| c.created_at < c.discussion.assignments.find_by_user_id(id).updated_at }
end

def create_new_invoice!
  invoice = invoices.build
  order_item_options.delete_if{ |o| o.price == 0 }.map{ |o| invoice.invoice_lines.build(:order_item_id => o.order_item.id, :description => o.order_item.name, :unit_price => o.price) }
  invoice.save!
end