form_tag for search bar with Rails 3.0.5

I have a controller and view that should be providing a search bar
that brings up that brings up a selected record on submission. I have
tried several variations, including just specifying the assets_path,
but usually end up with either an error or a submission to the index
action, rather than the show action. Currently, I have the following
in my index.html.haml:

= form_tag({:controller => 'assets', :action => 'show'}, :method
=> :GET) do
  .field
    =label_tag('Job
Number').titleize

%br/

=number_field_tag :id
  .actions
    =submit_tag 'Search', :name => nil

This gives me the following error:

  No route matches {:controller=>"assets", :action=>"show"}

$ rake routes | fgrep asset )
              assets GET /
assets(.:format)
{:action=>"index", :controller=>"assets"}
                     POST /
assets(.:format)
{:action=>"create", :controller=>"assets"}
           new_asset GET /assets/
new(.:format)
{:action=>"new", :controller=>"assets"}
          edit_asset GET /assets/:id/
edit(.:format)
{:action=>"edit", :controller=>"assets"}
               asset GET /
assets/:id(.:format)
{:action=>"show", :controller=>"assets"}
                     PUT /
assets/:id(.:format)
{:action=>"update", :controller=>"assets"}
                     DELETE /
assets/:id(.:format)
{:action=>"destroy", :controller=>"assets"}

How can I get a form_tag to take the user to /asset/123 (or whatever)
as intended?

Routing happens based on the url, not on form parameters. You might
try posting to a search action that would bounce them to the
appropriate show action. Equally you could wire up some javascript to
craft the correct url client side.

Fred