Dynamic Select Box Rails code

gistfile1.rb

# create new rails app
# rails new dynamic_select_boxes -m https://raw.github.com/RailsApps/rails3-application-templates/master/rails3-haml-html5-template.rb

# create models:
# rails g model genre name:string
# rails g model artist name:string genre_id:integer
# rails g model song title:string artist_id:integer

# rake db:migrate

# db/seeds.rb
3.times do |x|
  genre  = Genre.find_or_create_by_name(:name => "Genre #{x}")
  3.times do |y|
    artist = Artist.find_or_create_by_name(:name => "Artist #{x}.#{y}", :genre => genre)
    3.times do |z|
      Song.find_or_create_by_title(:title => "Song #{x}.#{y}.#{z}",  :artist => artist)
    end
  end
end

# app/models/artist.rb
class Artist < ActiveRecord::Base
  belongs_to :genre

  has_many :songs

  attr_accessible :genre_id, :name, :genre
end

# app/models/genre.rb
class Genre < ActiveRecord::Base
  attr_accessible :name

  has_many :artists
  has_many :songs, :through => :artists
end

# app/models/songs.rb
class Song < ActiveRecord::Base
  belongs_to :artist

  attr_accessible :artist_id, :title, :artist
end

# app/controllers/home_controller.rb
class HomeController < ApplicationController
  def index
    @genres  = Genre.all
    @artists = Artist.all
    @songs   = Song.all
  end

  def update_artists
    # updates artists and songs based on genre selected
    genre = Genre.find(params[:genre_id])
    # map to name and id for use in our options_for_select
    @artists = genre.artists.map{|a| [a.name, a.id]}.insert(0, "Select an Artist")
    @songs   = genre.songs.map{|s| [s.title, s.id]}.insert(0, "Select a Song")
  end

  def update_songs
    # updates songs based on artist selected
    artist = Artist.find(params[:artist_id])
    @songs = artist.songs.map{|s| [s.title, s.id]}.insert(0, "Select a Song")
  end
end

# app/views/home/index.html.haml
= collection_select(nil, :genre_id,  @genres,  :id, :name, {:prompt   => "Select a Genre"}, {:id => 'genres_select'})
%br
= collection_select(nil, :artist_id, @artists, :id, :name, {:prompt   => "Select an Artist"}, {:id => 'artists_select'})
%br
= collection_select(nil, :song_id, @songs, :id, :title, {:prompt   => "Select a Song"}, {:id => 'songs_select'})

:javascript
  $(document).ready(function() {
    $('#genres_select').change(function() {
      $.ajax({
        url: "#{update_artists_path}",
        data: {
          genre_id : $('#genres_select').val()
        },
        dataType: "script"
      });
    });
    $('#artists_select').change(function() {
      $.ajax({
        url: "#{update_songs_path}",
        data: {
          artist_id : $('#artists_select').val()
        },
        dataType: "script"
      });
    });
  });

# app/views/home/update_artists.js.haml
$('#artists_select').html("#{escape_javascript(options_for_select(@artists))}");
$('#songs_select').html("#{escape_javascript(options_for_select(@songs))}");

# app/views/home/update_songs.js.haml
$('#songs_select').html("#{escape_javascript(options_for_select(@songs))}");

# config/routes.rb
DynamicSelectBoxes::Application.routes.draw do
  get 'home/update_artists', :as => 'update_artists'
  get 'home/update_songs', :as => 'update_songs'
  root :to => "home#index"
end

# rake db:seed

# rails s