User-editable to_param value

I have a model that has an overriden to_param method returning the (unique) name of a record. This works quite fine, however with one caveat - the user can edit the name.

If I have record #1 with name="abc" and record #2 with name="xyz", then a user editing record #2 and changing name to "abc" will get an error upon saving as the validates_uniqueness_of constraint is violated. However when Rails constructs the edit.html.erb page again, it uses the unvalidated data - including to to_param which is now linking everything to record #1 ("abc"). Consequent saves thus 开发者_运维问答act on record #1 instead of record #2.

What would be the recommended best practice to prevent this horrendous result? Should I reset the name value before redirecting upon an error (but what if the name was okay and the error was elsewhere) or should I change my views to manually insert the id instead of using the automatics of Rails?

Probably the easiest thing to do would be to not rely on the name attribute but instead another attribute that is hidden from the user.

eg. if you had a permalink:string column on the model you could do something like:

Class ModelName < ActiveRecord::Base

  before_save :update_permalink

  validates_presence_of :name    

  def to_param
    permalink
  end

  private
  def update_permalink
    self.permalink = name.parameterize
  end
end