dynamically showing data based on different selection

I have the same situation where the users selects a room, then
storage , then sub compartment each with it's own unique dataset.
[Room]\/ [Storage type]\/ [Sub storage]\/ [Substorage]\/

The storage model uses the "acts_as_tree" for hierarchy.

it's a patch (if there is a better way to do it I'll be glad to
refactor it):

<% if !storages.empty?%>
<% type_url = "'/storages/get_selected_type/' +
this[this.selectedIndex].value "%>
<% select_array = storages.collect {|storage| [ storage.type_and_name,
storage.id ]}%>
<%=select "storage","id", select_array,
    options = {:prompt => "- Select -"},
    html_options={:onChange => "new Ajax.Request(#{type_url},
                  { asynchronous:true,
                                      evalScripts:true ,

                Element.hide('storage_children'); },

<%= spinner_tag("spinner_storage") %>

I am creating an Ajax request on the change event, this calls returns
the next selection dropdown.
(p.s. the spinner tag is just an helper method to return a spinner).

Hope this helps.
Jonathan Gross.