auto complete

I saw an example of the auto complete field sending a ajax request in
this format that allows a method in the controller to catch all auto
complete ajax requests:

'/rails/app/auto_complete_for/sample_origin'

but when I use it, the request is

'/rails/app/auto_complete_for_sample_origin'

My template says this

<%=text_field_with_auto_complete :sample, c, {:skip_style=>true}%>

How can I change it so that the request is '/rails/app/
auto_complete_for/sample_origin' ?

I changed the url in the macros helper file:

:url => { :action => "auto_complete_for", :id=>"#{object}_#{method}" }

  def text_field_with_auto_complete(object, method, tag_options = {},
completion_options = {})
    (completion_options[:skip_style] ? "" : auto_complete_stylesheet)