using form_for with a singular model - ruby-on-rails

Question

I have a Wizard model that the client references w/o an ID (it's saved in the session), so I've created a singular resource for :show and :update. I want the admin to have access to all instances of that model via index so admin can delete strays, so I've added a plural resources for :index and :destroy. The index and destroy works, but I can't figure out the right arguments to pass to form_for in the update view.
The setup
# config/routes.rb
WTest::Application.routes.draw.do
resource :wizard, :only => [:show, :update]
resources :wizards, :only => [:index, :destroy]
...
end
resulting in
$ rake routes
wizards GET /wizards(.:format) {:action=>"index", :controller=>"wizards"}
wizard DELETE /wizards/:id(.:format) {:action=>"destroy", :controller=>"wizards"}
GET /wizard(.:format) {:action=>"show", :controller=>"wizards"}
PUT /wizard(.:format) {:action=>"update", :controller=>"wizards"}
This sets up routes the way I'd expect.
The question (revised since original post)
In the console:
>> app.wizard_path
raises the error ActionController::RoutingError: No route matches {:action=>"destroy", :controller=>"wizards"}
Why is this? Have I set up my routes incorrectly? I need to specify :url => wizard_path for form_for() in the wizards's update view.
The details
If I specify an explicit path in my call to form_for:
# app/view/wizards/update.html.erb
<%= form_for #wizard, :url => wizard_path do |f| %>
<%= f.submit %>
<% end %>
... then attempting to render this for gets an error on the form_for line:
No route matches {:action=>"destroy", :controller=>"wizards"}
I have no idea why it's trying to match the destroy action. How do I get the form to submit to the {action=>"update", :controller=>"wizards"} route?
(By the way, I looked at bug 267, and I don't think it is the same as what I'm observing. But if it is this bug, is there a workaround?)

Answer 1

Carrying on the long tradition of answering my own questions (meh!), I think I figured it out. If my analysis is wrong, I'd be happy to give someone else the checkmark...
The cause of the problem
Look at the output of rake routes
$ rake routes
wizards GET /wizards(.:format) {:action=>"index", :controller=>"wizards"}
wizard DELETE /wizards/:id(.:format) {:action=>"destroy", :controller=>"wizards"}
GET /wizard(.:format) {:action=>"show", :controller=>"wizards"}
PUT /wizard(.:format) {:action=>"update", :controller=>"wizards"}
The path method 'wizard_path' is ambiguous: it can either refer to the DELETE clause, in which case it needs an :id argument (wizard_path(22)), or it can refer to the GET and PUT clauses, in which case it doesn't take an ID argument.
The solution
So my solution was to create a route specifically for deletion. My revised routes.rb file now reads:
resources :wizards, :only => [:index]
resource :wizard, :only => [:show, :update]
match 'wizard/:id' => 'wizards#destroy', :via => :delete, :as => :delete_wizard
and rake routes now produces:
$ rake routes
wizards GET /wizards(.:format) {:action=>"index", :controller=>"wizards"}
wizard GET /wizard(.:format) {:action=>"show", :controller=>"wizards"}
PUT /wizard(.:format) {:action=>"update", :controller=>"wizards"}
delete_wizard DELETE /wizard/:id(.:format) {:controller=>"wizards", :action=>"destroy"}
I needed to make a one-line change to the delete link in wizards/index.html.erb to use the new delete_wizard_path, but everything works now.