gistfile1.rb

# model

class Post < ActiveRecord::Base

  after_create :set_permalink
  
  def set_permalink
    self.permalink ||= self.title.parameterize
    self.save
  end
  
end

# controller

class PostsController < ApplicationController
  
  
  def show
    @post = Post.where(permalink: params[:id]).first
  end
  
end