Validates_uniqueness_of and attr_readonly

Rails
1

I notice that I always want to prevent the unique key of a table from
being changed. Does that mean I always have to have attr_readonly right
after validates_uniqueness_of ? Is there a single function that
replaces both of these but has the same affect?

Thanks.

Developing with Rails 2.3.2; Ruby 1.8.7 (2009-04-08 patchlevel 160)
[powerpc-darwin9]