Marcelo,
I'm trying to figure out why you'd want to use method_missing to load an object from the session...
If you're already typing:
obj = session_object_Usuario
Then it seems easier, faster, and more secure to define an accessor:
# application.rb
def current_usuario @current_usuario ||= (session[:usuario_id] ? Usuario.find(session[:usuario_id]) : nil) end helper_method :current_usuario
Hope this helps.