为什么我不能得到rake db：迁移到ruby.railstutorial.org工作

我决定完成教程.在我创建一个新应用程序并添加新用户：string email：string然后在app目录中执行rake db：migrate之后,我得到了这个输出：

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>'

我正在使用RVM太ruby 1.9.2和rails 3.0.7,如教程中所示.
有什么想法吗？

解决方法

另一种解决方案是在启动新的rails项目之前在Gemfile中要求rake 0.8.7.

# Gemfile
gem 'rake','0.8.7',:require => 'rake'

然后运行bundle install