无法使用Rails 3.2.6启动WEBrick

Question

I update my Rails version 3.2.3 to 3.2.6. After running the server getting following error:

=> Booting WEBrick
=> Rails 3.2.6 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Exiting
/usr/local/lib/ruby/gems/1.9.1/gems/activerecord-3.2.6/lib/active_record/dynamic_matchers.rb:50:in `method_missing': undefined method `instance' for #<Class:0x9844050> (NoMethodError)
    from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.6/lib/active_model/observing.rb:86:in `instantiate_observer'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.6/lib/active_model/observing.rb:59:in `block in instantiate_observers'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.6/lib/active_model/observing.rb:59:in `each'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.6/lib/active_model/observing.rb:59:in `instantiate_observers'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activerecord-3.2.6/lib/active_record/railtie.rb:117:in `block (2 levels) in <class:Railtie>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:36:in `instance_eval'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:36:in `execute_hook'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:26:in `block in on_load'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:25:in `each'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:25:in `on_load'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activerecord-3.2.6/lib/active_record/railtie.rb:116:in `block in <class:Railtie>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:34:in `call'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:34:in `execute_hook'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:43:in `block in run_load_hooks'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:42:in `each'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/lazy_load_hooks.rb:42:in `run_load_hooks'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/application/finisher.rb:59:in `block in <module:Finisher>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/initializable.rb:30:in `instance_exec'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/initializable.rb:30:in `run'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/initializable.rb:55:in `block in run_initializers'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/initializable.rb:54:in `each'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/initializable.rb:54:in `run_initializers'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/application.rb:136:in `initialize!'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/railtie/configurable.rb:30:in `method_missing'
    from /home/prasanna/Projects/Petcare/config/environment.rb:5:in `<top (required)>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:in `require'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:in `block in require'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:236:in `load_dependency'
    from /usr/local/lib/ruby/gems/1.9.1/gems/activesupport-3.2.6/lib/active_support/dependencies.rb:251:in `require'
    from /home/prasanna/Projects/Petcare/config.ru:4:in `block in <main>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:51:in `instance_eval'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:51:in `initialize'
    from /home/prasanna/Projects/Petcare/config.ru:1:in `new'
    from /home/prasanna/Projects/Petcare/config.ru:1:in `<main>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:40:in `eval'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/builder.rb:40:in `parse_file'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/server.rb:200:in `app'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/commands/server.rb:46:in `app'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/server.rb:301:in `wrapped_app'
    from /usr/local/lib/ruby/gems/1.9.1/gems/rack-1.4.1/lib/rack/server.rb:252:in `start'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/commands/server.rb:70:in `start'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/commands.rb:55:in `block in <top (required)>'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/commands.rb:50:in `tap'
    from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.6/lib/rails/commands.rb:50:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

environment.rb

# Load the rails application
require File.expand_path('../application', __FILE__)

# Initialize the rails application
Petcare::Application.initialize!

Answer 1

This is because Rails 3.x has problem with Ruby 1.9.1. Try updating your Ruby to 1.9.3.

Source: http://guides.rubyonrails.org/getting_started.html

Answer 2

Do you have any observers? If so make sure that they inherit from ActiveModel::Observer . If they are custom classes, make sure they include Singleton module.