Namespaced controller causes error in Rails-3 - ruby-on-rails-3

Question

I am using ActsAsTaggableOn to add tagging to my application. In addition to the features i get from this gem, I would also like to add a TagsController and basically treat tags as any other resource in my app.
I have created tags_controller.rb which contains
class ActsAsTaggableOn::TagsController < ApplicationController
# ...
end
and in my routes.rb i have added
resources :tags, :module => :acts_as_taggable_on
When I run rake routes i get
tags GET /tags(.:format) {:action=>"index", :controller=>"acts_as_taggable_on/tags"}
POST /tags(.:format) {:action=>"create", :controller=>"acts_as_taggable_on/tags"}
new_tag GET /tags/new(.:format) {:action=>"new", :controller=>"acts_as_taggable_on/tags"}
edit_tag GET /tags/:id/edit(.:format) {:action=>"edit", :controller=>"acts_as_taggable_on/tags"}
tag GET /tags/:id(.:format) {:action=>"show", :controller=>"acts_as_taggable_on/tags"}
PUT /tags/:id(.:format) {:action=>"update", :controller=>"acts_as_taggable_on/tags"}
DELETE /tags/:id(.:format) {:action=>"destroy", :controller=>"acts_as_taggable_on/tags"}
… which all looks reasonable to me.
However, when I hit localhost:3000/tags i get this error:
LoadError (Expected MyApp/tags_controller.rb to define TagsController)
If I try to evaluate ActsAsTaggableOn::TagsControllerin the console I get basically the same error:
LoadError: Expected MyApp/app/controllers/tags_controller.rb to define TagsController
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:492:in `load_missing_constant'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:183:in `block in const_missing'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:181:in `each'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:181:in `const_missing'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:503:in `load_missing_constant'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:183:in `block in const_missing'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:181:in `each'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.4/lib/active_support/dependencies.rb:181:in `const_missing'
from (irb):1
from ~/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands/console.rb:44:in `start'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands/console.rb:8:in `start'
from ~/.rvm/gems/ruby-1.9.2-p180/gems/railties-3.0.4/lib/rails/commands.rb:23:in `'
from script/rails:6:in `require'
from script/rails:6:in `'
What am I doing wrong?

Answer 1

Rails expects modules and classes to be in their namespace's directory. So you should move your controller, views and helpers in an acts_as_taggable_on directory:
app/controllers/acts_as_taggable_on/tags_controller.rb
app/views/acts_as_taggable_on/tags/index.html.erb
etc.
I'm not sure why you want this namespace. If you only want to create REST actions on an existing model, you can generate a scaffold_controller. For example:
rails generate scaffold_controller Tag name:string

Answer 2

Michaël is right about the directory structure for namespaced controllers.
That being said, a controller does not have to be in the same namespace as a model. On the contrary, you can have a controller named SomeController working with a model named SomeModel. Have you already tried to drop the namespace from the controller class and see what goes wrong?