Rails Ruby on Rails

i'm trying to generate a show url for a model for which the route defined is:

match '/model_x/:slug', :to => 'model_xs#show', :as => 'model_x', :via => 'get' resources :model_x, :except => ["show"]

rake routes shows me:

                model_x GET    /model_xs/:slug(.:format)                      {:controller=>"model_xs", :action=>"show"}
                model_xs GET    /model_xs(.:format)                           {:action=>"index", :controller=>"model_xs"}
                model_xs POST   /model_xs(.:format)                           {:action=>"create", :controller=>"model_xs"}
             new_model_x GET    /model_xs/new(.:format)                       {:action=>"new", :controller=>"model_xs"}
            edit_model_x GET    /model_xs/:id/edit(.:format)                  {:action=>"edit", :controller=>"model_xs"}
                 model_x PUT    /model_xs/:id(.:format)                       {:action=>"update", :controller=>"model_xs"}
                 model_x DELETE /model_xs/:id(.:format)                       {:action=>"destroy", :controller=>"model_xs"}

expected:

model_x_path(ModelX.find_by_slug('slug-for-model-x-1')) should give me '/model_xs/slug-for-model-x-1'

actual:

model_x_path(ModelX.find_by_slug('slug-for-model-x-1')) gives me '/model_xs/1'

this route is invalid as i have added :except => ["show"] to the resource route and defined routing to action show only by slug in the url.

even, model_x_path(:slug => 'slug-for-model-x-1') doesn't work.