Class variable reset with rails / spring

Question

I've a class defined as such:

class PublicationJob < ActiveJob::Base
  def self.jobs
    @jobs ||= Hash{|h, k| h[k] = []}
  end
  def self.register(format, job_class)
    jobs[format] << job_class
  end
  # [...]
end

To register different job classes, I put in an initializer:

PublicationJob.register(:tex, SaveJob)
PublicationJob.register(:saved_tex, TexJob)
#...

The in the rails console I try:

PublicationJob.jobs
#> {:tex => [SaveJob], :saved_tex => [TexJob]}

But if I exit the console (Ctrl-D) then restart it, at some point the hash will be empty!

Why is the class variable reset in this case?

I use rails 4.2.1 and spring, and I know that if I kill/stop spring it works again for some time. Is it related to spring?

Are you making modifications to files? Because spring reloads these files, and even restarts the application in some cases, causing your data to get wiped. — codingbunny, Apr 17 '15 at 08:38
I update some files in the app directory, but not even the publication_job :/ — Jaffa, Apr 17 '15 at 08:46
yeah, that could be enough for Spring to reload your app, depending on what you have changed. Thus wiping your data — codingbunny, Apr 17 '15 at 08:51
But if spring reloads the app, then why doesn't it reload the initializer as well ? — Jaffa, Apr 17 '15 at 08:52
look at https://github.com/rails/spring#class-reloading it explains why the data changes. — codingbunny, Apr 17 '15 at 08:55
Thanks a lot. "So to avoid this problem, don't save off references to application constants in your initialization code." In other words, this mean I can't initialize my application. Great ! — Jaffa, Apr 17 '15 at 09:06

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

Okay, so this was entirely Spring related, and I fixed it by removing spring.

Thanks to @NekoNova who pointed me to the right part of the documentation, I found that:

This saves off the first version of the User class, which will not be the same object as User after the code has been reloaded:

[...]

So to avoid this problem, don't save off references to application constants in your initialization code.

In other words, I can't initialize my classes using initializers, because althought it'll work in production, it won't work in development.

score 2 · Answer 2 · answered Feb 17 '17 at 15:02

I know this is rather old, but I have encountered this issue a couple of times, and feel that you don't have to abandon spring if you set class level variables at initialization.

All you need to do is re-assign them in a spring ".after_fork" block. So for the above issue, place in a "config/spring.rb" file, the following:

if ("Spring".constantize rescue nil)
  Spring.after_fork do
    PublicationJob.register(:tex, SaveJob)
    PublicationJob.register(:saved_tex, TexJob)
  end
end

This will reset those variables after spring completes the fork and reloading code. I wrap it in a check to ensure that Spring is available, which it likely won't be in production.

Class variable reset with rails / spring

2 Answers2