Rails 4 Heroku 资产：预编译失败

Question

我有一个奇怪的情况，突然面临预编译失败，老实说，由于某种原因我看不到这个问题。

我在这里添加了一个包含日志和参考文件的要点 https://gist.github.com/malagodia/8506722

让我困惑的是，我阅读了 Heroku 关于数据库连接的建议，并明确确保 application.rb 包含

config.assets.initialize_on_precompile = false

这里是日志输出错误，完整日志就大意了

Running: rake assets:precompile
       rake aborted!
       undefined method `[]=' for nil:NilClass
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/config/initializers/database_connection.rb:7:in `block (2 levels) in <top (required)>'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:38:in `instance_eval'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:38:in `execute_hook'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:28:in `block in on_load'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:27:in `each'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:27:in `on_load'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/config/initializers/database_connection.rb:5:in `block in <top (required)>'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:36:in `call'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:36:in `execute_hook'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:45:in `block in run_load_hooks'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:44:in `each'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/lazy_load_hooks.rb:44:in `run_load_hooks'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/application/finisher.rb:62:in `block in <module:Finisher>'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/initializable.rb:30:in `instance_exec'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/initializable.rb:30:in `run'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/initializable.rb:55:in `block in run_initializers'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/initializable.rb:54:in `run_initializers'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/application.rb:215:in `initialize!'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/railtie/configurable.rb:30:in `method_missing'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/config/environment.rb:5:in `<top (required)>'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `block in require'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:214:in `load_dependency'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.2/lib/active_support/dependencies.rb:229:in `require'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/application.rb:189:in `require_environment!'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/application.rb:250:in `block in run_tasks_blocks'
       /tmp/build_2826537d-5a5c-43f7-b792-45112618d3df/vendor/bundle/ruby/2.0.0/gems/sprockets-rails-2.0.1/lib/sprockets/rails/task.rb:54:in `block (2 levels) in define'
       Tasks: TOP => environment
       (See full trace by running task with --trace)  !  !     Precompiling assets failed.  !

 !     Push rejected, failed to compile Ruby app

heroku 指出的附加痕迹 ~ $ rake assets:precompile --trace
** 调用资产：预编译（first_time）
** 调用资产：环境（first_time）
** 执行资产：环境
** 调用环境 (first_time)
** 执行环境
** 执行资产：预编译

Answer 1

我最近从 Rails 4 升级到 4.1 时遇到了这个问题。

为了解决这个问题，我刚刚删除了文件database_connection.rb。由于 Heroku 在 Concurrency and Database Connections in Ruby with ActiveRecord 上的文章，我得到了这个文件。

希望对你有帮助！

Answer 2

我相信您的config 值是nil，因为在您预编译资产时数据库（或环境中的任何其他内容）不可用，因此您应该尽量避免与数据库相关的任何事情在那个阶段。情况描述here。

他们描述的解决方案只是“不要那样做”：

“一旦你隔离了错误，你必须通过不依赖环境变量和预编译时存在的数据库来修复它。”

Answer 3

我的情况是，我忘记更新 application.css 的扩展名以包含 .scss。所以，我猜，sprockets 试图编译一个不存在的 .scss 文件；因此 nil 错误。

我通过运行“RAILS_ENV=production bundle exec rake assets:precompile”在本地但在生产环境中编译我的资产（根据 Heroku 文档：https://devcenter.heroku.com/articles/rails-asset-pipeline）并查看最后几行输出来识别错误（输出比将完整的应用程序推送到 Heroku 更干净、更快捷）：

NoMethodError: nil:NilClass 的未定义方法 `[]' （在 /other_stuff/my_app/app/assets/stylesheets/application.css 中）

我注意到了 .css 扩展名并添加了 .scss 来修复错误。