为什么在 environment.rb 中需要此 gem 时出现错误？

Question

我按照here 的步骤安装了composite_primary_keys gem。当我尝试通过

在文件的最底部（在“结束”之后）要求 environment.rb 中的 gem 时

require 'composite_primary_keys'

我在启动服务器时得到这个

"69125"
=> Booting Mongrel
=> Rails 2.3.4 application starting on http://127.0.0.1:3002
/Library/Ruby/Site/1.8/rubygems.rb:270:in `activate': You have a nil object when you didn't expect it! (NoMethodError)
You might have expected an instance of Array.
The error occurred while evaluating nil.map
 from /Library/Ruby/Site/1.8/rubygems.rb:296:in `activate'
 from /Library/Ruby/Site/1.8/rubygems.rb:295:in `each'
 from /Library/Ruby/Site/1.8/rubygems.rb:295:in `activate'
 from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:35:in `require'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:156:in `require'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:521:in `new_constants_in'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:156:in `require'
 from /path/to/www/config/environment.rb:54
 from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
 from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:156:in `require'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:521:in `new_constants_in'
 from /path/to/www/vendor/rails/activesupport/lib/active_support/dependencies.rb:156:in `require'
 from /path/to/www/vendor/rails/railties/lib/commands/server.rb:84
 from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `gem_original_require'
 from /Library/Ruby/Site/1.8/rubygems/custom_require.rb:31:in `require'
 from ./script/server:3
 from -e:2:in `load'
 from -e:2

知道为什么会这样吗？

Answer 1

试着把它放在你的 environment.rb 中，像这样：

Rails::Initializer.run do |config|

  config.gem 'composite_primary_keys'

end