ruby on rails - Make attributes mass assignable only during creation

Question

Is it possible to have an attribute that is only mass-assignable during the creation of a model object?

For example, the username attribute should be mass-assignable when creating the object, but not after that (it should be read-only).

Answer 1

This is what attr_readonly does:

class User < ActiveRecord::Base
  attr_readonly :username
end

u = User.create(:username => 'dude')
u.username # => 'dude'

u.update_attributes(:username => 'dudette')
u.reload.username # => 'dude'