Why my rails is not auto-loading the app folder? - ruby-on-rails

Question

I just start using rails and now doing some basic drills to handle requests. I've created the project with rails new (project_name) --api --skip-active-record and following this video: https://www.youtube.com/watch?v=QojnRc7SS9o, since I don't want to use database yet so I added the --skip-active-record
...After tons of uninitialized errors, I added this line in application.rb
config.after_initialize do
# it should be defined in 'application_controller.rb'
puts "def: #{defined? ApplicationController}" # => nil
end
then I run rails s it says it's undefined(aka nil)...
Of course I can require the app folder manually, but it seems just reinvent the wheel, any way to fix this?
Additional info I run with the command that googled from another article, maybe will help:
>> ruby bin/rails runner "ActiveSupport::Dependencies.autoload_paths.each{|line| puts line}"
F:/Programming/RoR/api_test/app/channels
F:/Programming/RoR/api_test/app/controllers
F:/Programming/RoR/api_test/app/controllers/concerns
F:/Programming/RoR/api_test/app/jobs
F:/Programming/RoR/api_test/app/mailers
F:/Programming/RoR/api_test/app/models
F:/Programming/RoR/api_test/app/models/concerns
F:/Programming/RoR/api_test/test/mailers/previews
Edit: The full error trace of the uninitiated error:
Started GET "/api/v0/handshake" for ::1 at 2019-07-11 17:24:30 +0800
ActionController::RoutingError (uninitialized constant Api::V0::HandshakeController):
activesupport (5.2.3) lib/active_support/inflector/methods.rb:285:in `const_get'
activesupport (5.2.3) lib/active_support/inflector/methods.rb:285:in `block in constantize'
activesupport (5.2.3) lib/active_support/inflector/methods.rb:281:in `each'
activesupport (5.2.3) lib/active_support/inflector/methods.rb:281:in `inject'
activesupport (5.2.3) lib/active_support/inflector/methods.rb:281:in `constantize'
actionpack (5.2.3) lib/action_dispatch/http/request.rb:88:in `controller_class_for'
actionpack (5.2.3) lib/action_dispatch/http/request.rb:81:in `controller_class'
actionpack (5.2.3) lib/action_dispatch/routing/route_set.rb:46:in `controller'
actionpack (5.2.3) lib/action_dispatch/routing/route_set.rb:32:in `serve'
actionpack (5.2.3) lib/action_dispatch/journey/router.rb:52:in `block in serve'
actionpack (5.2.3) lib/action_dispatch/journey/router.rb:35:in `each'
actionpack (5.2.3) lib/action_dispatch/journey/router.rb:35:in `serve'
actionpack (5.2.3) lib/action_dispatch/routing/route_set.rb:840:in `call'
rack (2.0.7) lib/rack/etag.rb:25:in `call'
rack (2.0.7) lib/rack/conditional_get.rb:25:in `call'
rack (2.0.7) lib/rack/head.rb:12:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (5.2.3) lib/active_support/callbacks.rb:98:in `run_callbacks'
actionpack (5.2.3) lib/action_dispatch/middleware/callbacks.rb:26:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
railties (5.2.3) lib/rails/rack/logger.rb:38:in `call_app'
railties (5.2.3) lib/rails/rack/logger.rb:26:in `block in call'
activesupport (5.2.3) lib/active_support/tagged_logging.rb:71:in `block in tagged'
activesupport (5.2.3) lib/active_support/tagged_logging.rb:28:in `tagged'
activesupport (5.2.3) lib/active_support/tagged_logging.rb:71:in `tagged'
railties (5.2.3) lib/rails/rack/logger.rb:26:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/request_id.rb:27:in `call'
rack (2.0.7) lib/rack/runtime.rb:22:in `call'
activesupport (5.2.3) lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (5.2.3) lib/action_dispatch/middleware/static.rb:127:in `call'
rack (2.0.7) lib/rack/sendfile.rb:111:in `call'
railties (5.2.3) lib/rails/engine.rb:524:in `call'
puma (3.12.1) lib/puma/configuration.rb:227:in `call'
puma (3.12.1) lib/puma/server.rb:660:in `handle_request'
puma (3.12.1) lib/puma/server.rb:474:in `process_client'
puma (3.12.1) lib/puma/server.rb:334:in `block in run'
puma (3.12.1) lib/puma/thread_pool.rb:135:in `block in spawn_thread'
My controller file (path: app/controllers/api/v0/handshake.rb)
module Api
module V0
class HandshakeController < ApplicationController
def index
render json: {status: 'SUCCESS', message: 'Hello World!'}, status: :ok
end
end
end
end
and the routes.rb
Rails.application.routes.draw do
namespace 'api' do
namespace 'v0' do
resources :handshake
end
end
end

Answer 1

OK I got it. The problem is my filename is unmatched with the rail's autoload file structure as it says here, after I renamed handshake.rb to handshake_controller.rb and it worked