10

我正在我的 Rails 应用程序中实现类似纸迹的功能。为了做到这一点，我在 YAML 中序列化对象。我有item_at_version方法，基本上可以YAML::load(cached_object)- 这很好用，但是，我不知道为什么，有时它会返回undefined class/module _class name_. 它适用于 Event、Conversation、Note 等模型，但没有任何原因，它似乎会为 Dataset、Comment、Student 等模型抛出该错误（我试图为此找到任何模式，但没有任何运气） .

我正在使用 rails 3.2.8、ruby 1.9.3p327、psych 作为 YAML 引擎（Psych::Version 返回 1.3.4）。

附言。当我在该文件顶部添加 require 'model_name' 时，它就像一个魅力。

有什么想法我应该更改/添加什么才能使其正常工作？

编辑：我可以分享的代码不多：

def item_at_version
  YAML::load(cached_object)
end

但也许回溯会很有趣：

~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `path2class'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `resolve_class'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:219:in `visit_Psych_Nodes_Mapping'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:15:in `visit'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:5:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:20:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:238:in `visit_Psych_Nodes_Document'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:15:in `visit'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/visitor.rb:5:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:20:in `accept'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/nodes/node.rb:35:in `to_ruby'
~/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych.rb:128:in `load'
app/models/history_version.rb:7:in `item_at_version'
app/controllers/history_controller.rb:8:in `show'
actionpack (3.2.8) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (3.2.8) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.8) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.8) lib/active_support/callbacks.rb:502:in `_run__1697733322876708236__process_action__1122943786273335015__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.8) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.8) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.8) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.8) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.8) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.8) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.8) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.8) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.8) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:600:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/cookies.rb:339:in `call'
activerecord (3.2.8) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.8) lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `_run__2589517259026276185__call__1369641113040304056__callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.8) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.8) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.8) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
bugsnag (1.2.5) lib/bugsnag/rack.rb:35:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.8) lib/rails/rack/logger.rb:26:in `call_app'
railties (3.2.8) lib/rails/rack/logger.rb:16:in `call'
quiet_assets (1.0.1) lib/quiet_assets.rb:20:in `call_with_quiet_assets'
actionpack (3.2.8) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.8) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.8) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.8) lib/rails/engine.rb:479:in `call'
railties (3.2.8) lib/rails/application.rb:223:in `call'
railties (3.2.8) lib/rails/railtie/configurable.rb:30:in `method_missing'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:147:in `handle'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:99:in `rescue in block (2 levels) in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:96:in `block (2 levels) in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:86:in `each'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:86:in `block in start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:66:in `loop'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:66:in `start'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/lib/nack/server.rb:13:in `run'
~/Library/Application Support/Pow/Versions/0.4.0/node_modules/nack/bin/nack_worker:4:in `<main>'
4

3 回答 3

14

在YAML.dumpRuby 中用于序列化对象时，类名用作 Yaml 标记的一部分，以便在加载对象时可以使用正确的类。例如：

require 'yaml'

class Foo; end

puts YAML.dump Foo.new

生产

--- !ruby/object:Foo {}

当您YAML.load在该字符串上使用时，Psych 知道要为反序列化对象实例化哪个类。

如果您尝试调用YAML.load指定尚未定义的类的 Yaml 字符串，则会收到错误消息：

require 'yaml'

# No Bar class has been defined
YAML.load '--- !ruby/object:Bar {}'

产生：

/Users/matt/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `path2class': undefined class/module Bar (ArgumentError)
    from /Users/matt/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/psych/visitors/to_ruby.rb:312:in `resolve_class'
...

这是因为 Psych 需要创建 class 的实例Bar，但没有可用的类的定义。这解释了为什么require 'whatever'在加载 Yaml 之前添加有效 - 现在 Ruby 已经加载了类的定义，因此可以创建它的实例（请注意，在 Ruby 中类名和文件名之间没有明确的联系，这只是约定）。

因此，解决方案是确保当您从 Yaml 加载任何 Ruby 对象时，您已经需要任何可能包含该 Yaml 中任何类的定义的文件。

于 2012-12-06T19:08:53.807 回答
2

马特的回答提供了必要的细节。

但是当我对代码进行更改然后执行一些任务时，它会反序列化一些数据，而无需页面加载（在 AJAX 中），然后它会失败并出现相同的错误。

使用require_dependency比require自动加载更改要好。

如果是模块（未使用 测试class）并使用 YAML 进行反序列化，您还可以在反序列化之前实例化您的模块require以解决问题。看这里。

资料来源： Github 中的SO answer和Psych 问题报告

PS：这个问题只存在于开发中，因为config.cache_classes在生产中启用。

于 2016-06-02T07:23:01.113 回答
1

修改马特的回答。代替基于纯哈希的解决方案（Psych 团队似乎对此没有兴趣），修改标题字符串以去除对象分类。我只是用下面的代码做到了这一点。

yamltext = File.read("somefile","r")
yamltext.sub!(/^--- \!.*$/,'---')
hash = YAML.load(yamltext)

如果输入流由具有不同对象分类器的多个文档组成（我不知道这是否有效），这可能会失败（我不知道）。

于 2016-07-22T18:42:33.747 回答