autosave no longer a valid option for belongs_to?

The Rails API doc ( says that :autosave is still a valid option for belongs_to in the latest version of Rails. However, a look at the activerecord/lib/active_record/associations.rb (line 1590) reveals that it is not in the @@valid_keys_for_belongs_to_association array. I also noticed that it's not in the ActiveRecord API doc (

Does anyone have any more information on this? What is the current best practice for persisting your child objects when saving a parent object? Here's an example:

class PaymentMethod < ActiveRecord::Base   belongs_to :billing_address, :class_name => "Address" end class Address < ActiveRecord::Base   validates_presence_of :line_one end class PaymentMethodsController < ActionController::Base   def update     @pm = PaymentMethod.find(params[:id])     @pm.billing_address.line_one = params[:billing_address][:line_one]     # ...     if       # ...     end   end end

Thanks in advance.