No route matches "/admin" error - ruby-on-rails-3

Question

I am writing my first application in rails and here is what I did
C:\Personal\rails\demo>ruby -v
ruby 1.9.2p136 (2010-12-25) [i386-mingw32]
C:\Personal\rails\demo>rails -v
Rails 3.0.5
C:\Personal\rails\demo>rails generate model book
invoke active_record
create db/migrate/20110325190010_create_books.rb
create app/models/book.rb
invoke test_unit
create test/unit/book_test.rb
create test/fixtures/books.yml
C:\Personal\rails\demo>rake db:migrate
(in C:/Personal/rails/demo)
== CreateBooks: migrating ====================================================
-- create_table(:books)
-> 0.0000s
== CreateBooks: migrated (0.0000s) ===========================================
C:\Personal\rails\demo>rails generate controller admin
create app/controllers/admin_controller.rb
invoke erb
create app/views/admin
invoke test_unit
create test/functional/admin_controller_test.rb
invoke helper
create app/helpers/admin_helper.rb
invoke test_unit
create test/unit/helpers/admin_helper_test.rb
Then i edited the admin_controller.rb as follows:
class AdminController < ApplicationController
scaffold :book
end
Here is the routes.rb file
Demo::Application.routes.draw do
# The priority is based upon order of creation:
# first created -> highest priority.
# Sample of regular route:
# match 'products/:id' => 'catalog#view'
# Keep in mind you can assign values other than :controller and :action
# Sample of named route:
# match 'products/:id/purchase' => 'catalog#purchase', :as => :purchase
# This route can be invoked with purchase_url(:id => product.id)
# Sample resource route (maps HTTP verbs to controller actions automatically):
# resources :products
# Sample resource route with options:
# resources :products do
# member do
# get 'short'
# post 'toggle'
# end
#
# collection do
# get 'sold'
# end
# end
# Sample resource route with sub-resources:
# resources :products do
# resources :comments, :sales
# resource :seller
# end
# Sample resource route with more complex sub-resources
# resources :products do
# resources :comments
# resources :sales do
# get 'recent', :on => :collection
# end
# end
# Sample resource route within a namespace:
# namespace :admin do
# # Directs /admin/products/* to Admin::ProductsController
# # (app/controllers/admin/products_controller.rb)
# resources :products
# end
# You can have the root of your site routed with "root"
# just remember to delete public/index.html.
# root :to => "welcome#index"
# See how all your routes lay out with "rake routes"
# This is a legacy wild controller route that's not recommended for RESTful applications.
# Note: This route will make all actions in every controller accessible via GET requests.
# match ':controller(/:action(/:id(.:format)))'
end
However, when I go to http://localhost:3000/admin, I get a "No route matches "/admin"" error. I noticed that my routes.rb has only the commented lines. Did I do something wrong?

Answer 1

You have not added a route for admin, why are all your routes commented out.
if admin is a resource add this line
resources :admin
Also in your controller you will need an index method and index view file because http://localhost:3000/admin will take you there

Answer 2

Try removing the comment from this line:
match ':controller(/:action(/:id(.:format)))'

Answer 3

Note: This answer is for the case when above mentioned points are met yet you keep seeing this error. It was Rails 3.2 and Ruby 2.3.8
Problem definition:
I successfully logged in using admin creds. When page landed on /admin I saw No route matches [GET] "/admin" error page. I hit my head everywhere and used all my knowledge. Also, generated routes and grep but no admin route was published.
$ rake routes | grep admin
but only devise related admin routes were published. And then I read the warning about the routes which I noticed later, which goes like
ActiveAdmin: ActiveAdmin::DatabaseHitDuringLoad: Your file, app/admin/account_tags.rb (line 4),
caused a database error while Active Admin was loading. This is most common
when your database is missing or doesn't have the latest migrations applied.
To prevent this error, move the code to a place where it will only be run
when a page is rendered. One solution can be, to wrap the query in a Proc.
Original error message: PG::UndefinedTable: ERROR: relation "account_tags" does not exist
Solution
I ran rake db:migrate and restarted the server, the problem was gone.