[RUBY] Rails uninitialized constant A simple checklist for error resolution

What is this

Despite doing Rails as it is, I'm addicted to uninitialized constant errors, so I'll put together a checklist here.

Conclusion

The following three items should be checked.

1. Does the file name and class name match? --Does the file path and module definitions match? --Are Rails reading the file?

I will write the details below.

Does the file name and class name match?

If the following class exists, the file name must be qiita_user.rb.

class QiitaUser
  def hoge
  end
end

Do the file path and module definitions match?

If there is a nested class in the following module, the path will be something like ** / v1 / auth / user.rb.

class V1::Auth::User
end

OR

module V1
  module Auth
    class User
    end
  end
end

Are you letting Rails read the file?

If you want to add a folder other than the Rails default folder, you need to define the path to the added folder in autoload path. Suppose you add ʻapp / lib / hoge / foo.rb. In this case, you need to add the autoload path to config / application.rb` in the following form.

module App
  class Application < Rails::Application
    #abridgement
    
    config.autoload_paths += Dir.glob("#{config.root}/app/lib")
  end
end