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.

Answer 1

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.