爲什麼在environment.rb中需要這個gem時會出錯？

Question

我按照步驟here並安裝了composite_primary_keys gem。當我嘗試要求的environment.rb寶石在文件的最底部（「結束」後）通過

require 'composite_primary_keys' 

我得到這個啓動服務器

"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 

知道爲什麼這時候正在發生？

Answer 1

嘗試把它在你的environment.rb中這樣的：

Rails::Initializer.run do |config| 

    config.gem 'composite_primary_keys' 

end