Ajaxed pages frequently need to update many parts of the page within ajax callbacks. Here I'll outline how we use jQuery and Rails do this on Mavenlink. Our approach encodes behavior declaratively in markup and minimizes client-side logic.
ActiveRecord's update_attribute() method is useful for setting a single attribute value while bypassing validation.
You may not know, however, that when invoked on a new record, update_attribute() saves the record, including all the fields, and bypassing validation for all fields.
This can lead to some unwelcome surprises. For example, acts_as_list uses update_attribute(), so if you're using acts_as_list, watch out for unexpected, unvalidated saves when using new records within the list.
Thanks to Adam Milligan for the heads-up.