Rails - Jan 2006 - Saving ActiveRecord objects that are composed of other objects

I''ve got two pretty simple model objects Page and PagePart. Page 
has_many PageParts and PageParts belong_to Pages.

When updating PageParts for a specific Page I''d like to be able to do:

   page.parts[x].content = ''changed''
   page.save

and expect that should the validation pass the changed page part would 
be saved as well, but this doesn''t seem to work for me. Why
doesn''t
ActiveRecord automatically update objects that are composed of other 
objects when saving?

I''d rather not write:

   if page.save
     page.parts.each { part.save }
   end

because should a failure occur when saving the parts I don''t want the 
page to be saved. Of course I could override the #save method and use 
transactions for this, but I''d rather not do that if ActiveRecord 
provides something built in. Am I missing something?

--
John Long
http://wiseheartdesign.com