gistfile1.builder

# It's pretty easy to set a custom method as the basis of your friendly_id if
# you want to incorporate information from another model in the friendly_id.
class City < ActiveRecord::Base

  belongs_to :state
  has_friendly_id :city_and_state, :use_slugs => true

  # This will return something like "San Francisco, California". It can be used
  # as a display name in your views, and also as the basis of the friendly_id
  # because it will be processed by the plugin to remove spaces, punctuation,
  # capital letters, etc.
  def display_name
    "#{state.name.titleize}, #{name.titleize}"
  end
end

# The only major problem with this, is that if you state's friendly_id ever
# changes, the city's friendly_id will not be updated. Depending on your app,
# this may or may not be a problem.

# It's often better to simply rely on the tools that Rails provides: use a
# nested route, and just give both models a friendly_id:

# Models
class State < ActiveRecord::Base
  has_friendly_id :name, :use_slugs => true
end

class City < ActiveRecord::Base
  has_friendly_id :name, :use_slugs => true
end

# Route. Then `state_city_url(@state, @city)` will give you something like
# http://example.org/states/california/cities/san-francisco
map.resources :states, :has_many => :cities

# Somewhere in your cities controller:
@state = State.find(params[:state_id])
@city = @state.cities.find(params[:id])