我是 Ruby on Rails 和 MongoDB 的新手，但我想开始运行我在 MongoDB 上制作的任何 Rails 应用程序。
我正在关注 MongoDB 网站 ( http://docs.mongodb.org/ecosystem/tutorial/model-data-for-ruby-on-rails/ ) 上的简短教程，但在尝试开始时遇到了障碍Rails 服务器。
在对 nameError 消息进行了大量谷歌搜索之后，我仍然不明白它为什么存在以及我需要做什么。
PGW:tindow ~~$ rails s
=> Booting WEBrick
=> Rails 4.2.0 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/usr/local/tindow/config/initializers/database.rb:1:in `<top (required)>': uninitialized constant MongoMapper (NameError)
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/engine.rb:652:in `block in load_config_initializer'
from /Library/Ruby/Gems/2.0.0/gems/activesupport-4.2.0/lib/active_support/notifications.rb:166:in `instrument'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/engine.rb:651:in `load_config_initializer'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/engine.rb:616:in `block (2 levels) in <class:Engine>'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/engine.rb:615:in `each'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/engine.rb:615:in `block in <class:Engine>'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:30:in `instance_exec'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:30:in `run'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:55:in `block in run_initializers'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:150:in `block in tsort_each'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:183:in `block (2 levels) in each_strongly_connected_component'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:210:in `block (2 levels) in each_strongly_connected_component_from'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:219:in `each_strongly_connected_component_from'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:209:in `block in each_strongly_connected_component_from'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:44:in `each'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:44:in `tsort_each_child'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:203:in `each_strongly_connected_component_from'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:182:in `block in each_strongly_connected_component'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:180:in `each'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:180:in `each_strongly_connected_component'
from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/tsort.rb:148:in `tsort_each'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/initializable.rb:54:in `run_initializers'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/application.rb:352:in `initialize!'
from /usr/local/tindow/config/environment.rb:6:in `<top (required)>'
from /usr/local/tindow/config.ru:3:in `require'
from /usr/local/tindow/config.ru:3:in `block in <main>'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `instance_eval'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:55:in `initialize'
from /usr/local/tindow/config.ru:in `new'
from /usr/local/tindow/config.ru:in `<main>'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:49:in `eval'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:49:in `new_from_string'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/builder.rb:40:in `parse_file'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:299:in `build_app_and_options_from_config'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:208:in `app'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:61:in `app'
from /Library/Ruby/Gems/2.0.0/gems/rack-1.6.0/lib/rack/server.rb:336:in `wrapped_app'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:139:in `log_to_stdout'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/server.rb:78:in `start'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:80:in `block in server'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `tap'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `server'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
from /Library/Ruby/Gems/2.0.0/gems/railties-4.2.0/lib/rails/commands.rb:17:in `<top (required)>'
from /usr/local/tindow/bin/rails:8:in `require'
from /usr/local/tindow/bin/rails:8:in `<top (required)>'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/client/rails.rb:27:in `load'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/client/rails.rb:27:in `call'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/client/command.rb:7:in `call'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/client.rb:26:in `run'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/bin/spring:48:in `<top (required)>'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/binstub.rb:11:in `load'
from /Library/Ruby/Gems/2.0.0/gems/spring-1.3.0/lib/spring/binstub.rb:11:in `<top (required)>'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /usr/local/tindow/bin/spring:16:in `<top (required)>'
from bin/rails:3:in `load'
from bin/rails:3:in `<main>'