Modify values after update/create

Hi Guys,

I’m playing with nested attributes (accepts_nested_attributes_for).
There are two models:

Location
Event (Fields: title, at_date, is_booked, …)

Locations can have multiple events, and the events can be added and
removed dynamically in the location-form with javascript (based on this
tutorial: http://www.railsforum.com/viewtopic.php?id=28447&p=1)

The field is_booked should be true or false, depending on several
conditions (f.e. at_date has a specific value). Is there any way to
change these values after update_attributes() or should I solve this
with javascript in the view? Is there any other way? Is it
possible/advisable to change the params()-array?

Thanks a lot!