YAML :: load引发未定义的类/模块错误
我正在我的rails应用程序中实现类似于纸张跟踪的function。 为了做到这一点，我在YAML中序列化对象。 我有item_at_version方法，它基本上是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_ 。 它适用于像Event，Conversation，Note等模型，但没有任何理由，它似乎为像Dataset，Comment，Student这样的模型抛出了这个错误（我试图找到任何模式，没有任何运气） 。
我使用rails 3.2.8，ruby 1.9.3p327，psych作为YAML Engine（Psych :: Version返回1.3.4）。
PS。 当我在该文件的顶部添加require’model_name’时，它就像一个魅力。
任何想法我应该改变/添加什么来使这个工作？
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 `'
当您使用YAML.dump序列化Ruby中的对象时，类名称将用作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
产生
--- !ruby/object:Foo {}
当您在该字符串上使用YAML.load时，Psych知道要为反序列化对象实例化的类。
如果您尝试在指定尚未定义的类的Yaml字符串上调用YAML.load ，则会收到错误：
require 'yaml' # No Bar class has been defined YAML.load '--- !ruby/object:Bar {}'
生产：
/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需要创建类Bar的实例，但没有可用类的定义。 这解释了为什么在加载Yaml之前添加require 'whatever' what require 'whatever' – 现在Ruby已经加载了类的定义，因此可以创建它的实例（注意Ruby中的类名和文件名之间没有确定的链接，它只是惯例）。
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中可能包含的任何类的定义的文件。
马特的答案提供了必要的细节。
但是当我对代码进行更改然后执行某项任务时，会对某些数据进行反序列化，而不会加载页面（在AJAX中），然后它会以相同的错误失败。
最好使用require_dependency而不是require来自动加载您的更改。
对于模块（未经过class测试）和使用YAML进行反序列化，您还可以在反序列化之前实例化模块，并使用require修复问题。 看这里。
资料来源： Github的 SO答案和心理问题报告
PS：此问题仅在开发中持续存在，因为在生产中启用了config.cache_classes 。
修改马特的答案 。 代替基于纯哈希的解决方案（Psych团队似乎没有兴趣），修改标题字符串以去除对象分类。 我只是使用以下代码完成此操作。
yamltext = File.read("somefile","r") yamltext.sub!(/^--- \!.*$/,'---') hash = YAML.load(yamltext)
如果输入流包含具有不同对象分类器的多个文档（我不知道这是否有效），这可能会失败（我不知道）。