How to properly set up, make or include concern in Rails

Question

Usually, concerns are located in

app/controllers/concerns.

But I want to make and separate concerns for admin side.

app/controllers/admin/concerns

Given I set up some sample codes,

# app/controllers/admin/concerns/test.rb
module Test
  extend ActiveSupport::Concern

  included do
    before_action :test
  end

  def test
    render json: 'test concern'
  end
end

# ALSO tried...,

module Admin
  module Test
    extend ActiveSupport::Concern

    included do
      before_action :test
    end

    def test
      render json: 'test concern'
    end
  end
end

# then include like, include Admin::Test

How to properly call or include the test concern in my admin controller.

class Admin::ShopsController < Admin::BaseController
   include Admin::Test # doing this,
   # got uninitialized constant Admin::Test
end

Answer 1

Related explanation has been written in official guide.

All right, Rails has a collection of directories similar to $LOAD_PATH in which to look up post.rb. That collection is called autoload_paths and by default it contains:

Any existing second level directories called app/*/concerns in the application and engines.

https://guides.rubyonrails.org/autoloading_and_reloading_constants.html

The reason why app/controllers/admin/concerns isn't loaded is it's not a second level directory.

Since files in the second level concerns directory are automatically loaded, in this case you sould put the test.rb file in the app/controllers/concerns/admin.

Or adding app/controllers/admin/concerns to autoload path, but it's not highly recommended because this is out of rails design pattern.