我有一个非常基本的Rails 3.1rc6应用程序，基本上只有Devise，CanCan和rails_admin，以及一些非常简单的模型。
在开发环境中rails_admin工作正常，我可以点击localhost:3000/admin，在我的管理员用户登录后，我可以看到所有数据并进行管理。
但是当我部署到Heroku并试图点击appname.herokuapp.com/admin时，我得到“您正在寻找的页面不存在。您可能输错了地址或页面可能已移动”。这是Heroku日志的尾巴：
app[web.1]:
app[web.1]:
app[web.1]: Started GET "/admin" for 79.157.xx.xx at 2011-08-24 12:15:52 +0000
app[web.1]:
app[web.1]: ActionController::RoutingError (No route matches {:controller=>"home"}):
heroku[router]: GET appname.herokuapp.com/admin dyno=web.1 queue=0 wait=0ms service=7ms status=404 bytes=728
app[web.1]: app/controllers/application_controller.rb:5:in `block in <class:ApplicationController>'
app[web.1]:
app[web.1]:
app[web.1]: cache: [GET /admin] miss
app[web.1]: Processing by RailsAdmin::MainController#index as HTML
app[web.1]: Completed 404 Not Found in 2ms
所有其他路线（基本上设计路线）都可以正常工作。
在我的本地计算机上运行Thin in production（我在Heroku中使用的网络服务器）时，我得到了同样的结果：
$ bundle exec rails server thin -e production
=> Booting Thin
=> Rails 3.1.0.rc6 application starting in production on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Sprockets::Environment#static_root is deprecated
>> Thin web server (v1.2.11 codename Bat-Shit Crazy)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:3000, CTRL+C to stop
cache: [GET /admin] miss
Started GET "/admin" for 127.0.0.1 at 2011-08-24 13:49:42 +0200
Processing by RailsAdmin::MainController#index as HTML
Completed 404 Not Found in 3ms
ActionController::RoutingError (No route matches {:controller=>"home"}):
app/controllers/application_controller.rb:5:in `block in <class:ApplicationController>'
Rendered /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/actionpack-3.1.0.rc6/lib/action_dispatch/middleware/templates/rescues/routing_error.erb within rescues/layout (0.9ms)
在浏览器上
Routing Error
No route matches {:controller=>"home"}
这是我的routes.rb
root :to => "home#index"
devise_for :users
resources :users, :only => :show
mount RailsAdmin::Engine => '/admin', :as => 'rails_admin'
初始化/ rails_admin.rb
RailsAdmin.config do |config|
config.authorize_with :cancan
config.reload_between_requests = false
end
这里是heroku上的路线
$ heroku run rake routes
Running rake routes attached to terminal... up, run.8
root / {:controller=>"home", :action=>"index"}
new_user_session GET /users/sign_in(.:format) {:action=>"new", :controller=>"devise/sessions"}
user_session POST /users/sign_in(.:format) {:action=>"create", :controller=>"devise/sessions"}
destroy_user_session GET /users/sign_out(.:format) {:action=>"destroy", :controller=>"devise/sessions"}
user_password POST /users/password(.:format) {:action=>"create", :controller=>"devise/passwords"}
new_user_password GET /users/password/new(.:format) {:action=>"new", :controller=>"devise/passwords"}
edit_user_password GET /users/password/edit(.:format) {:action=>"edit", :controller=>"devise/passwords"}
PUT /users/password(.:format) {:action=>"update", :controller=>"devise/passwords"}
cancel_user_registration GET /users/cancel(.:format) {:action=>"cancel", :controller=>"devise/registrations"}
user_registration POST /users(.:format) {:action=>"create", :controller=>"devise/registrations"}
new_user_registration GET /users/sign_up(.:format) {:action=>"new", :controller=>"devise/registrations"}
edit_user_registration GET /users/edit(.:format) {:action=>"edit", :controller=>"devise/registrations"}
PUT /users(.:format) {:action=>"update", :controller=>"devise/registrations"}
DELETE /users(.:format) {:action=>"destroy", :controller=>"devise/registrations"}
user GET /users/:id(.:format) {:action=>"show", :controller=>"users"}
rails_admin /admin {:to=>RailsAdmin::Engine}
最后这里是本地路线......同样的！
$ rake routes
root / {:controller=>"home", :action=>"index"}
new_user_session GET /users/sign_in(.:format) {:action=>"new", :controller=>"devise/sessions"}
user_session POST /users/sign_in(.:format) {:action=>"create", :controller=>"devise/sessions"}
destroy_user_session GET /users/sign_out(.:format) {:action=>"destroy", :controller=>"devise/sessions"}
user_password POST /users/password(.:format) {:action=>"create", :controller=>"devise/passwords"}
new_user_password GET /users/password/new(.:format) {:action=>"new", :controller=>"devise/passwords"}
edit_user_password GET /users/password/edit(.:format) {:action=>"edit", :controller=>"devise/passwords"}
PUT /users/password(.:format) {:action=>"update", :controller=>"devise/passwords"}
cancel_user_registration GET /users/cancel(.:format) {:action=>"cancel", :controller=>"devise/registrations"}
user_registration POST /users(.:format) {:action=>"create", :controller=>"devise/registrations"}
new_user_registration GET /users/sign_up(.:format) {:action=>"new", :controller=>"devise/registrations"}
edit_user_registration GET /users/edit(.:format) {:action=>"edit", :controller=>"devise/registrations"}
PUT /users(.:format) {:action=>"update", :controller=>"devise/registrations"}
DELETE /users(.:format) {:action=>"destroy", :controller=>"devise/registrations"}
user GET /users/:id(.:format) {:action=>"show", :controller=>"users"}
rails_admin /admin {:to=>RailsAdmin::Engine}
有关为什么rails_admin路由在开发中工作但未在生产中工作的任何想法，我该怎么做才能解决这个问题？
如果它有帮助，当我在生产中运行WEBrick时，它会失败
$ rails s production
Exiting
/home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:237:in `require': no such file to load -- rack/handler/production (LoadError)
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:237:in `block in require'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:223:in `block in load_dependency'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:636:in `new_constants_in'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:223:in `load_dependency'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/activesupport-3.1.0.rc6/lib/active_support/dependencies.rb:237:in `require'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/rack-1.3.2/lib/rack/handler.rb:63:in `try_require'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/rack-1.3.2/lib/rack/handler.rb:16:in `get'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/rack-1.3.2/lib/rack/server.rb:269:in `server'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/railties-3.1.0.rc6/lib/rails/commands/server.rb:59:in `start'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/railties-3.1.0.rc6/lib/rails/commands.rb:54:in `block in <top (required)>'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/railties-3.1.0.rc6/lib/rails/commands.rb:49:in `tap'
from /home/mccoy/.rvm/gems/ruby-1.9.2-p290@talleres-r31/gems/railties-3.1.0.rc6/lib/rails/commands.rb:49:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'
但我认为这更像是我身边的宝石/配置问题而不是任何相关问题。适用于开发环境。
答案 0 :(得分：2)
经过进一步（并且非常痛苦）的调查后，我发现这是由cancan引起的，而不是rails_admin引起的。
生产数据库中的测试用户没有分配正确的角色，因此无权访问rails_admin。这引发了相应的AccessDenied异常，该异常由application_controller.rb中的
处理rescue_from CanCan::AccessDenied do |exception|
redirect_to root_url, :alert => exception.message
end
但由于某种原因，redirect_to root_url因上述路由错误而失败。在阅读了这个未解决的问题https://github.com/ryanb/cancan/issues/443
开发数据库中的测试用户具有正确的角色，可以正确访问rails_admin，这使得调试非常令人沮丧。
至少现在我走的是正确的道路！