问题描述
我正在Rails应用程序中实现类似纸质追踪的功能.为此，我要在YAML中序列化对象.我有item_at_version方法，该方法基本上可以执行YAML::load(cached_object) －效果很好，但是我不知道为什么，有时返回undefined class/module _class name_.它可以与事件，对话，注释等模型配合使用，但没有任何原因，对于数据集，注释，学生模型(似乎已经为它找到了任何模式，没有任何运气)似乎都抛出了该错误.
I’m implementing paper trail like feature in my rails app. In order to do this, I’m serializing object in YAML. I’ve got item_at_version method, which basically does YAML::load(cached_object) – this works pretty well, however, I have no idea why, sometimes it returns undefined class/module _class name_.It works with models like Event, Conversation, Note, and many more, but without any reason, it seems to throw that error for models like Dataset, Comment, Student (I’ve tried to find any pattern for that, without any luck).
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).
I’m using rails 3.2.8, ruby 1.9.3p327, psych as YAML Engine (Psych::Version returns 1.3.4).
Ps.当我在该文件顶部添加require'model_name'时，它就像一个超级按钮.
Ps. When I add require 'model_name' on top of that file, it works like a charm.
任何想法我应该更改/添加什么才能使它正常工作?
Any ideas what should I change/add to get this working?
我没有太多可以分享的代码:
There’s no much code which I can share:
def item_at_version
YAML::load(cached_object)
end
但是回溯也许会很有趣:
But maybe backtrace would be interesting:
~/.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>'
推荐答案
在Ruby中使用YAML.dump序列化对象时，该类名称将用作Yaml标记的一部分，以便在以下情况下可以使用正确的类加载对象.例如:
When you use YAML.dump to serialize an object in Ruby, the class name is use as part of the Yaml tag so that the correct class can be used when loading the object. For example:
require 'yaml'
class Foo; end
puts YAML.dump Foo.new
产生
--- !ruby/object:Foo {}
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.
When you use YAML.load on that string, Psych knows what class to instantiate for the deserialized object.
如果您尝试在Yaml字符串上调用YAML.load，该字符串指定了尚未定义的类，则会收到错误消息:
If you try to call YAML.load on a Yaml string that specifies a class that hasn’t been defined, then you will get the error:
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需要创建类Bar的实例，但是没有可用的类定义.这解释了为什么在加载Yaml之前添加require 'whatever'可以起作用的原因-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，Ruby中类名和文件名之间没有确定的链接，这只是约定而已) ).
This is because Psych needs to create an instance of class Bar, but doesn’t have the definition of the class available. This explains why adding require 'whatever' before loading the Yaml works – now Ruby has the definition of the class loaded and so can create an instance of it (note that there is no definitive link between class name and file name in Ruby, it’s just convention).
因此，解决方案是确保从Yaml加载任何Ruby对象时，已经需要任何可能包含该Yaml中任何类的定义的文件.
The solution therefore is to make sure that when you’re loading any Ruby objects from Yaml you have already required any files that may contain definitions of any classes potentially in that Yaml.
这篇关于YAML :: load引发未定义的类/模块错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！