Easy way to support custom (human-written) URLs (helpful with SEO) using friendly_id

custom_url_exmaple.rb

class BlogPost < ActiveRecord::Base

  # This Model has, in addition to title and other usual fields, 
  # two fields for creating custom urls:
  # 
  # :use_custom_url, :boolean
  # :custom_url, :string

  validates :title, :presence => true, :uniqueness => true

  has_friendly_id :title_or_custom, :use_slug => true
  
  protected
  
  def title_or_custom
    use_custom_url ? custom_url : title
  end
end