[Rails] Concerns, Engines, Generators

rails concerns, ActiveSupport::Concern, rails engine, rails generators, mountable engine

정의

Concern은 모듈에 클래스 메서드와 콜백을 한 곳에 모으는 패턴. Engine은 별도 gem으로 분리 가능한 미니 Rails 앱. Generator는 코드 자동 생성 (모델, 컨트롤러, 마이그레이션 등). 셋 다 코드 재사용·모듈화 도구.

ActiveSupport::Concern

# app/models/concerns/trashable.rb
module Trashable
  extend ActiveSupport::Concern

  included do
    scope :trashed, -> { where.not(trashed_at: nil) }
    scope :not_trashed, -> { where(trashed_at: nil) }

    before_destroy :prevent_if_trashed
  end

  class_methods do
    def trash_count
      trashed.count
    end
  end

  # 인스턴스 메서드
  def trash!
    update!(trashed_at: Time.current)
  end

  def restore!
    update!(trashed_at: nil)
  end

  private

  def prevent_if_trashed
    throw :abort if trashed_at.present?
  end
end

class Post < ApplicationRecord
  include Trashable
end

class Comment < ApplicationRecord
  include Trashable
end

post.trash!
Post.trashed
Post.trash_count

included do ... end 블록 안의 모든 코드는 include하는 클래스 컨텍스트에서 실행 → scope, validation, callback 추가.

일반 module과 비교

# 일반 module
module Trashable
  def self.included(base)
    base.scope :trashed, -> { where.not(trashed_at: nil) }
    base.before_destroy :prevent_if_trashed
  end

  module ClassMethods
    def trash_count
      ...
    end
  end
end

class Post < ApplicationRecord
  include Trashable
  extend Trashable::ClassMethods
end

ActiveSupport::Concern이 boilerplate 제거.

의존성 해결

module A
  extend ActiveSupport::Concern
end

module B
  extend ActiveSupport::Concern
  include A    # A가 먼저 included됨
end

class Post
  include B    # B만 include하면 A도 자동
end

순서 자동 해결.

Controller Concern

# app/controllers/concerns/authentication.rb
module Authentication
  extend ActiveSupport::Concern

  included do
    before_action :authenticate_user!
    helper_method :current_user
  end

  private

  def current_user
    @current_user ||= User.find_by(id: session[:user_id])
  end

  def authenticate_user!
    redirect_to login_path unless current_user
  end
end

class ApplicationController < ActionController::Base
  include Authentication
end

Rails Engine

Mini Rails app을 gem으로.

rails plugin new my_engine --mountable

my_engine/
├── app/
│   ├── controllers/my_engine/
│   ├── models/my_engine/
│   └── views/my_engine/
├── config/routes.rb
├── lib/my_engine/engine.rb
└── my_engine.gemspec

engine.rb:

module MyEngine
  class Engine < ::Rails::Engine
    isolate_namespace MyEngine
  end
end

호스트 앱에서:

# Gemfile
gem "my_engine", path: "../my_engine"
# 또는 git/path 등

# config/routes.rb
mount MyEngine::Engine => "/my_engine"

URL: /my_engine/posts/...

자주 보는 Engine

• Devise (인증)
• Sidekiq Web UI (mount Sidekiq::Web => "/sidekiq")
• Mission Control (mount MissionControl::Jobs::Engine => "/jobs")
• Rails admin / ActiveAdmin (관리자 UI)
• Wagtail Ruby 버전: NO (Wagtail은 Django)

대규모 앱을 여러 모듈로 분리하는 데도 사용.

Generator

빌트인

bin/rails g model Post title:string body:text
bin/rails g controller Posts index show
bin/rails g migration AddSlugToPosts slug:string:uniq
bin/rails g scaffold Post title:string body:text
bin/rails g mailer UserMailer welcome
bin/rails g job CleanupJob
bin/rails g channel Chat
bin/rails g system_test posts

커스텀 Generator

bin/rails g generator service

# lib/generators/service/service_generator.rb
class ServiceGenerator < Rails::Generators::NamedBase
  source_root File.expand_path("templates", __dir__)

  def create_service_file
    template "service.rb.tt", "app/services/#{file_name}_service.rb"
  end

  def create_test_file
    template "service_test.rb.tt", "test/services/#{file_name}_service_test.rb"
  end
end

# lib/generators/service/templates/service.rb.tt
class <%= class_name %>Service
  def call
    # TODO
  end
end

사용:

bin/rails g service CreatePost
# app/services/create_post_service.rb 생성
# test/services/create_post_service_test.rb 생성

Generator 옵션

bin/rails g model Post --skip-migration --skip-test --skip-fixture

config/application.rb로 기본 옵션:

config.generators do |g|
  g.test_framework :rspec, fixture: false
  g.factory_bot dir: "spec/factories"
  g.skip_routes true
end

새 generator 호출 시 자동 적용.

자주 보는 Concern 패턴

Sluggable

module Sluggable
  extend ActiveSupport::Concern

  included do
    before_validation :generate_slug, on: :create
    validates :slug, presence: true, uniqueness: true
  end

  def to_param
    slug
  end

  private

  def generate_slug
    self.slug ||= title.parameterize
  end
end

Notifiable

module Notifiable
  extend ActiveSupport::Concern

  included do
    has_many :notifications, as: :notifiable, dependent: :destroy

    after_create_commit :notify_subscribers
  end

  private

  def notify_subscribers
    subscribers.each do |user|
      Notification.create!(user: user, notifiable: self)
    end
  end
end

Searchable

module Searchable
  extend ActiveSupport::Concern

  class_methods do
    def search(query)
      where("title ILIKE :q OR body ILIKE :q", q: "%#{query}%")
    end
  end
end

Concern 안티패턴

1. Concern으로 god module

module Post::Behaviors
  extend ActiveSupport::Concern
  # 300줄
end

작은 concern으로 분리.

2. concern 의존성

module A
  def call
    do_b   # B의 메서드 필요
  end
end

module B
  def do_b; ... end
end

class C
  include A    # B 빠뜨림 → 런타임 NoMethodError
  include B
end

명시적 include 의존 위험. 서비스 객체로 분리가 더 안전.

3. service object 대체

# 컨트롤러 concern으로 비즈니스 로직
module CreatePost
  def create_post(params)
    Post.transaction do
      post = Post.create!(params)
      Notification.create!(...)
      post
    end
  end
end

→ Service object 클래스가 더 명확:

class CreatePostService
  def call(params)
    Post.transaction do
      post = Post.create!(params)
      Notification.create!(...)
      post
    end
  end
end

Engine 함정

1. 호스트 앱과 라우트 충돌

mount MyEngine::Engine => "/"    # 충돌 가능
mount MyEngine::Engine => "/admin"    # 안전

2. asset compile

Engine asset도 host에서 collectstatic / asset compile 필요.

3. 의존성 관리

Engine의 gem 의존성이 host와 충돌. gemspec에서 정확한 버전.