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observer bug
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Rohit Arondekar- Milestone cleared.
- State changed from new to open
- Tag set to rails 3, activerecord, loaderror, observer
- Importance changed from to Low
Confirmed on Rails master on 1.9.2-RC1 too.
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Rohit Arondekar
This is a strange bug.
I added the following just before the exception is raised in activesupport/lib/active_support/dependencies.rb : 465
puts "For #{const_name}" puts "#{file_path}" puts "Loaded #{const_name}" if local_const_defined?(from_mod, const_name) puts "END"I get the following output in the console (truncated for clarity):
First Try:
ruby-1.9.2-rc1 > Bar For BarObserver /home/rohit/bugmash/newapp/app/models/bar_observer.rb Loaded BarObserver END For Bar /home/rohit/bugmash/newapp/app/models/bar.rb END LoadError: Expected /home/rohit/bugmash/newapp/app/models/bar.rb to define BarSecond Try:
ruby-1.9.2-rc1 > Bar For Bar /home/rohit/bugmash/newapp/app/models/bar.rb Loaded Bar END => Bar(id: integer, created_at: datetime, updated_at: datetime)So there must be something going on in require_or_load method. Could it be that it thinks Bar is already loaded because of BarObserver? Will take a look later but I thought I should put what I found in here, in case somebody else wants to take a crack at it.
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Rohit Arondekar
- Assigned user set to José Valim
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José ValimRohit put a
puts callerat the beginning of load_missing_constant error and it returned this: http://pastie.org/1037235By looking at this caller stack trace, is easier to grasp what is going on:
1) When you invoke Bar, it will trigger load_missing_constant(Bar);
2) Once Bar file is loaded, it will find and load ActiveRecord::Base, triggering a few hooks;
3) One of these ActiveRecord hooks is called instantiate_observer and it will cause BarObserver to be loaded through load_missing_constant(BarObserver);
4) BarObserver is then loaded and it will try to apply its hooks to the Bar class. We already asked Bar class to be loaded, but it hasn't happened yet, because we started to load ActiveRecord::Base, which loaded BarObserver which wants to load Bar once again. What happens at this point, is that Bar is loaded again by AS::Dependencies, causing for us to have two Bar references, but one of them is obviously invalid;
I'm not sure what is the proper fix here. By doing things lazy is stepping on our toes once again. :(
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José Valim
The issue could be easily avoided by forcing ActiveRecord::Base to be loaded before loading Bar:
irb > ActiveRecord::Base
irb > Bar.create #=> works -
Xavier NoriaA minimal example that depicts the circularity involved:
fxn@rails:~/tmp/h$ cat app/models/foo.rb class Foo < Bar end fxn@rails:~/tmp/h$ cat app/models/bar.rb class Bar end Foo fxn@rails:~/tmp/h$ script/rails runner Foo /home/fxn/rails/railties/lib/rails/commands/runner.rb:50: /home/fxn/rails/activesupport/lib/active_support/dependencies.rb:465:in `load_missing_constant': Expected /home/fxn/tmp/h/app/models/foo.rb to define Foo (LoadError) -
Xavier Noria
The issue is not a deadlock, that would work in MRI, but it implies two executions of foo.rb:
halmos:tmp fxn$ cat test_const_missing.rb def Object.const_missing(name) case name.to_s when 'Foo' load 'foo.rb' Foo when 'Bar' load 'bar.rb' Bar end end Foo halmos:tmp fxn$ cat foo.rb puts "in foo.rb" class Foo < Bar puts "defining Foo" end halmos:tmp fxn$ cat bar.rb puts "in bar.rb" class Bar puts "defining Bar" end Foo halmos:tmp fxn$ ruby test_const_missing.rb in foo.rb in bar.rb defining Bar in foo.rb defining Foo defining FooWhich is not good anyway (perhaps dependencies is complaining to prevent that issue?).
I wonder if this justifies not lazy loading Active Record, looks like this loop is unsolvable.
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José Valim
- State changed from open to resolved
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