我决定学习本教程。在我创建了一个新的应用程序并添加了新的user:string email:string，然后在应用程序目录中执行rake db:migrate之后，我得到了以下输出：
rake aborted!
undefined method `task' for #<DemoApp::Application:0x00000100e49e08>
/usr/local/rvm/gems/ruby-1.9.2-p180@rails3tutorial/gems/railties-3.0.7/lib/rails/application.rb:215:in `initialize_tasks'
/usr/local/rvm/gems/ruby-1.9.2-p180@rails3tutorial/gems/railties-3.0.7/lib/rails/application.rb:139:in `load_tasks'
/usr/local/rvm/gems/ruby-1.9.2-p180@rails3tutorial/gems/railties-3.0.7/lib/rails/application.rb:77:in `method_missing'
/Users/zigloo99/rails_projects/demo_app/Rakefile:7:in `<top (required)>'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/rake_module.rb:25:in `load'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/rake_module.rb:25:in `load_rakefile'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:495:in `raw_load_rakefile'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:78:in `block in load_rakefile'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:129:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:77:in `load_rakefile'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:61:in `block in run'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:129:in `standard_exception_handling'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/lib/rake/application.rb:59:in `run'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/gems/rake-0.9.0/bin/rake:31:in `<top (required)>'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/bin/rake:19:in `load'
/usr/local/rvm/gems/ruby-1.9.2-p180@global/bin/rake:19:in `<main>'
我使用的RVM也像教程中的ruby 1.9.2和rails 3.0.7。有什么想法吗？
之所以会发生这种情况，是因为最新版本的Rake（0.9.0）在Rails3.0应用程序上出现故障，我们目前正在等待可靠的修复。
现在，解决此错误的方法是在应用程序的Rakefile:中的load_tasks行之上添加此行
<AppName>::Application.send :include, ::Rake::DSL if defined?(::Rake::DSL)
另一个解决方案是在启动新的rails项目之前，需要Gemfile中的rake 0.8.7。
# Gemfile
gem 'rake', '0.8.7', :require => 'rake'
然后运行bundle install