Zeitwerk::NameError due to Module name in rails 7

Question

I recently upgraded my application from rails 6 to 7 and I am facing one issue due to zeitwerk naming convention. I have a below file which I want to autoload:

app/models/dw/hospital.rb

module DW
  class Hospital < DataWarehouse
    def self.columns
      super.reject{|column| column.name == 'tableau_user' }
    end
  end
end

I tried autoloading this file by adding the following line in my application.rb file:

config.autoload_once_paths << 'app/models/dw'

But when I am starting the server I am getting the following error:

expected file app/models/dw/hospital.rb to define constant Hospital, but didn't (Zeitwerk::NameError)

I'm not sure why this is throwing such error since the constant is already defined. I suspect it is because the module I have defined before the class. Please let me know if anybody how to fix this. I have been stuck at this far too long.

Alex · Accepted Answer · 2022-09-16T09:48:03.790

Because you've added app/models/dw to autoload paths, you have to define Hospital but your definition is namespaced DW::Hospital. You don't need to touch autoload config, app/models is already in autoload_paths:

>> ActiveSupport::Dependencies.autoload_paths
=> 
...
 "/home/alex/code/stackoverflow/app/jobs",
 "/home/alex/code/stackoverflow/app/mailers",
 "/home/alex/code/stackoverflow/app/models",   # <======
...

These are so called root directories. It means file structure relative to app/models have to correspond to module/class names.

So if you have dw/hospital.rb in any of the root directories you have to define Dw::Hospital, which you've defined already. You have to watch for inflections as well, it should be Dw, unless you have an acronym inflection rule or zeitwerk inflection:

>> "dw".camelize
=> "Dw"

ActiveSupport::Inflector.inflections(:en) do |inflect|
  inflect.acronym "DW" 
end  

>> "dw".camelize
=> "DW"

If you must nest root directories, you should have a really good reason:

# if you want it to be reloadable,
# use `autoload_paths` instead of `autoload_once_paths`
config.autoload_paths << Rails.root.join("app/models/dw")

# app/models/dw/hospital.rb
class Hospital
end

But as Xavier mentioned in the comment, there is no need for this configuration. Use the default config and don't complicate your set up unnecessarily.

Excellent answer. Let me add, to be clear, that there is no need to touch the configuration (please do remove that config.autoload_once_paths setting), and that this is covered in the migration HOWTO: https://guides.rubyonrails.org/classic_to_zeitwerk_howto.html#acronyms — Xavier Noria, Sep 16 '22 at 07:22
Alex and @XavierNoria Thankyou for you answer, it was really helpful. Although I had another question related to zeitwerk. Please answer if you know something about that. I have been stuck at this rails 7 upgrade for quite a while now. https://stackoverflow.com/questions/73754260/zeitwerk-not-autoloading-models-in-rails-7 — Dev V, Sep 17 '22 at 11:04

score 2 · Answer 2 · answered Sep 15 '22 at 20:57

Looks like the problem with uppercase

Normally PascalCase (aka CamelCase) class name must correspond to the snake_case file name. The same rule applies to namespaces and folders

But you have DW in dw folder (not Dw)

You can create some initializer like this

# config/initializers/zeitwerk.rb 

Rails.autoloaders.each do |autoloader|
  autoloader.inflector = Zeitwerk::Inflector.new
  autoloader.inflector.inflect(
    'dw' => 'DW',
    # other special cases
  )
end

Zeitwerk::NameError due to Module name in rails 7

2 Answers2