Rails Ruby on Rails

Comments and changes to this ticket

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  Stefan Siebel June 29th, 2010 @ 12:00 PM

  • Title changed from “Nested objects don't deserialized completely (Rails 3 beta 4)” to “Nested objects don't deserialize completely (Rails 3 beta 4)”
• 

  Aaron Patterson June 30th, 2010 @ 12:45 AM

  • Assigned user set to “Aaron Patterson”
  • Importance changed from “” to “Low”

  Could you possibly upload an app that has this error (and a test)? I'd like to take a look.

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  Stefan Siebel June 30th, 2010 @ 09:01 PM

  Hi Aaron,

  cool, thank you! Please see attached file. It looks like the issue is a little bit weird. I tried to reproduce it with a test, but apparently the test works fine.

  That's how you can reproduce the issue:

  1) Create a new user object through the UI (localhost:3000/users)
  2) load the rails console, type in:

  u = User.last
  u.preferences.test.kind_of? Something
  => false
  

  Another to reproduce it, only with rails console, without web UI:

  
  a = User.new
  a.save
  
  b = User.last
  b.preferences.test.kind_of? Something
  => true
  
  reload!
  
  b = User.last
  b.preferences.test.kind_of? Something
  => false
  

  Does that help?

  -Stefan

  • exampleapptar.gz 86.1 KB
• 

  Aaron Patterson June 30th, 2010 @ 11:50 PM

  • Tag changed from “activerecord rails3, serialize” to “activerecord rails3, serialize, yaml”
  • State changed from “new” to “invalid”

  Hey Stefan!

  Thanks for the sample application! I was indeed able to reproduce the problem, but unfortunately the problem isn't from Rails. I'll show you the fix for your code, then go in to detail about the problem.

  Just add this to the top of your photo_style.rb file:

  require 'style_element'
  

  The problem is that your class isn't defined at the time the YAML gets deserialized. You've taught Rails how to load the top level constant when you made the serialize :preferences, UserPreferences call. Unfortunately, it doesn't know how to load the other class. We can reproduce this behavior with a Ruby program like this:

  require 'yaml'
  
  class UserPreferences
  end
  
  p YAML.load DATA.read
  
  __END__
  --- !ruby/object:UserPreferences 
  test: !ruby/object:Something 
    a: 1
    b: 2
    c: 3
  

  You'll note that the output of this shows the same problem that the rails code is experiencing. If you were using Marshal to serialize and deserialize these objects, this case would actually result in an exception being raised. The reason an exception is raised with marshal is because it doesn't know the definition of that object, so it can't properly deserialize it.

  I believe this difference between Marshal and YAML to be a bug. The newer YAML parser in ruby 1.9 (psych) will raise an exception in this case, matching the behavior of Marshal. For example:

  require 'yaml'
  
  YAML::ENGINE.yamler = 'psych'
  
  class UserPreferences
  end
  
  p YAML.load DATA.read
  
  __END__
  --- !ruby/object:UserPreferences 
  test: !ruby/object:Something 
    a: 1
    b: 2
    c: 3
  

  If you run the above code using Ruby 1.9.2 you'll see the exception raised. That exception can give rails a chance to load the missing constant.

  I hope this explanation helps!

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  Stefan Siebel July 1st, 2010 @ 09:45 AM

  Excellent Aaron! Thank you!

  I already sort of expected it's something I'm doing wrong since I'm still pretty new to Ruby / Rails :-)

  Thanks again, I really appreciate!

  -Stefan.