Installing gem Stringex for Rails? Don't forget to migrate

I was setting up Stringex for my existing User model following the Readme (there aren't actually any installation instructions) and guessed I needed to add the gem to my Gemfile:

# Gemfile
gem "stringex"

And set up my models and controllers:

# user.rb
acts_as_url :name, :sync_url => true

def to_param
  url
end

# users_controller.rb
load_and_authorize_resource :find_by => :url

I am using CanCan here.

So it struck me, when I then received routing errors:

ActionController::RoutingError at /users
No route matches {:action=>"show", :controller=>"users", :id=>#<User id: 1, email: ...

Turns out, you need to add some columns first:

$ rails g migration AddUrlToUsers url:string:uniq

# 20130404102715_add_url_to_users.rb
class AddUrlToUsers < ActiveRecord::Migration
  def up
    add_column :users, :url, :string, :nil => false
    add_index :users, :url, :unique => true

    # You'll want to generate the URLs for all existing users:
    User.initialize_urls
  end

  def down
    remove_index :users, :url
    remove_column :users, :url
  end
end

But that's obvious, isn't it?

Follow-up: Redirecting old ID routes to new slugs