升级到rails 3.1.12后出错

Question

我刚从rails 3.1.11升级到3.1.12。我正在使用ruby 1.9.3。在我使用 rails s 启动服务器后，我收到以下错误

=> Booting WEBrick
=> Rails 3.1.12 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Uncaught exception: No such middleware to insert after: "ActionDispatch::ShowExceptions"

我的Gem文件位于

之下

source 'http://rubygems.org'
gem 'rails', '~> 3.1.12'
gem 'rake'
gem 'rack'
gem "haml"
gem "haml-rails"
gem 'mysql2'
gem 'airbrake'
gem 'newrelic_rpm'

问题在于newrelic_rpm和airbrake宝石。如果两者都被删除，应用程序工作。 使用newrelic_rpm我们会收到此错误。

Uncaught exception: undefined local variable or method `establish_connection' for ActiveRecord::Base:Class

使用airbrake我们会收到此错误

Uncaught exception: No such middleware to insert after: "ActionDispatch::ShowExceptions"