gistfile1.rb

# Careful with to_param

class Page < ActiveRecord::Base

  validates_presence_of :handle
  validates_uniqueness_of :handle
  validates_format_of :handle, :with => /^[a-z0-9-]+$/, :message => 'The handle can only contain lowercase letters, numbers and dashes.'

  def to_param
    handle
  end

end

# Make sure to capture the old handle on uniqueness validation errors.
# Otherwise, submitting the form after render with the same handle will
# submit to the duplicate address (i.e. /pages/my-page/edit) and override and 
# save both records with the new values

class PagesController < ApplicationController

  def update
    @page = Page.find(params[:id])
    old_handle = @page.handle
    respond_to do |format|
      if @page.update_attributes(params[:page])
        flash[:notice] = 'Page was successfully updated.'
        format.html { redirect_to edit_page_url }
      else
        @page.handle = old_handle
        format.html { render :action => "edit" }
      end
    end
  end

end