Observe Field Problem

Hi there!

I need to use observe field to change dynamically one select field based
on another select field:

here is the view:

<%= observe_field 'class', :url => { :action => 'update_list' },
:frequency => 0.25,
:update => 'nickname',
:with => 'tipid'

Class:<select name="<%= "#{name}[][#{name}_class]" %>" id="class">
<%= options_from_collection_for_select(Tiprod.find(:all),
"id","name", {:include_blank => true}) %>
Name:<select name="<%= "#{name}[][#{name}_data]" %>" id="nickname">

here is the controller

def update_list
@tipid = params[:tipid]
@products = Specprod.find(:all, :conditions => ['tiprif LIKE ?',

and here is the update_list.rhtml

<% for product in @products%>
<option value="<%= product.id %>"><%= product.name%></option>
<% end %>

inspired by:http://nealenssle.com/blog/2007/04/12/how-to-dynamically-update-form-

The observe_field helper just produces some javascript that does stuff
to the element with id class

You've got the call to observe_field before your select element, ie
it's trying to observe something that doesn't exist yet.