Dynamic dropdown

im working on the code in this link…
PullMonkey Blog » Blog Archive » Dynamic Select Boxes – Ruby on Rails

i cant able to dynamically select values in second and third dropdown
using onchange event … any suggestions pls…

index.rhtml is…

<%= javascript_include_tag :defaults %>

<%= collection_select(nil, :genre_id, @genres, :id, :name,
{:prompt => “Select a Genre”},
{:onchange =>" alert(‘sd’);"}) %>

<%= render :partial => 'artists', :object => @artists %>
<%= render :partial => 'songs', :object => @songs %>

controller is…

def update_artists
# updates artists and songs based on genre selected
@genre = Genre.find(params[:genre_id])
@artists = @genre.artists
@songs = @genre.songs

render :update do |page|
  page.replace_html'artists', :partial => 'artists'
  page.replace_html 'songs',   :partial => 'songs',   :object => 


if i select values in first drop down i cant get corresponding values
for second as well as for third… pls help