class ApplicationController < ActionController::Base
  before_action :set_locale
  after_action :log_activity
  around_action :wrap_in_transaction

  private

  def set_locale
    I18n.locale = params[:locale] || I18n.default_locale
  end

  def log_activity
    ActivityLog.create(user: current_user, action: action_name)
  end

  def wrap_in_transaction
    ActiveRecord::Base.transaction do
      yield
    end
  end
end

class ArticlesController < ApplicationController
  before_action :authenticate_user!, only: [:edit, :update, :destroy]

  def edit
    @article = Article.find(params[:id])
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  def destroy
    @article = Article.find(params[:id])
    @article.destroy
    redirect_to articles_path
  end

  private

  def authenticate_user!
    unless user_signed_in?
      flash[:alert] = "You need to sign in before continuing."
      redirect_to login_path
    end
  end
end

class ArticlesController < ApplicationController
  after_action :log_activity, only: [:create, :update, :destroy]

  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  def destroy
    @article = Article.find(params[:id])
    @article.destroy
    redirect_to articles_path
  end

  private

  def log_activity
    ActivityLog.create(user: current_user, action: action_name)
  end
end

class ArticlesController < ApplicationController
  around_action :wrap_in_transaction, only: [:create, :update, :destroy]

  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  def destroy
    @article = Article.find(params[:id])
    @article.destroy
    redirect_to articles_path
  end

  private

  def wrap_in_transaction
    ActiveRecord::Base.transaction do
      yield
    end
  end
end

class ArticlesController < ApplicationController
  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  private

  def article_params
    params.require(:article).permit(:title, :body)
  end
end

class ArticlesController < ApplicationController
  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  private

  def article_params
    params.require(:article).permit(:title, :body, author_attributes: [:name, :email])
  end
end

class ArticlesController < ApplicationController
  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  private

  def article_params
    if current_user.admin?
      params.require(:article).permit(:title, :body, :published_at)
    else
      params.require(:article).permit(:title, :body)
    end
  end
end

class ArticlesController < ApplicationController
  def create
    @article = Article.new(article_params)
    if @article.save
      redirect_to @article
    else
      render 'new'
    end
  end

  def update
    @article = Article.find(params[:id])
    if @article.update(article_params)
      redirect_to @article
    else
      render 'edit'
    end
  end

  private

  def article_params
    params.require(:article).permit(:title, :body, category_ids: [])
  end
end

class ArticlesController < ApplicationController
  def show
    @article = Article.find(params[:id])
    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @article }
    end
  end
end

/articles/1.html
/articles/1.json

Accept: application/json

class ArticlesController < ApplicationController
  def index
    @articles = Article.all
    respond_to do |format|
      format.html # index.html.erb
      format.csv { send_data @articles.to_csv, filename: "articles-#{Date.today}.csv" }
    end
  end
end

# ArticleモデルにCSV変換メソッドを追加
require 'csv'

class Article < ApplicationRecord
  def self.to_csv
    attributes = %w{id title body created_at updated_at}

    CSV.generate(headers: true) do |csv|
      csv << attributes

      all.each do |article|
        csv << attributes.map{ |attr| article.send(attr) }
      end
    end
  end
end

class ArticlesController < ApplicationController
  def show
    @article = Article.find(params[:id])
    respond_to do |format|
      format.html
      format.json { render json: @article, status: :ok }
    end
  rescue ActiveRecord::RecordNotFound
    respond_to do |format|
      format.html { redirect_to articles_path, alert: "Article not found." }
      format.json { render json: { error: "Article not found." }, status: :not_found }
    end
  end
end

class ArticlesController < ApplicationController
  def show
    @article = Article.find(params[:id])
    respond_to do |format|
      format.html
      format.json { render json: @article, status: :ok }
    end
    response.headers['Custom-Header'] = 'This is a custom header'
  end
end

class ApplicationController < ActionController::Base
  before_action :set_default_response_format

  private

  def set_default_response_format
    request.format = :json
  end
end

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, with: :record_not_found

  private

  def record_not_found
    render file: 'public/404.html', status: :not_found
  end
end

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound do
    render file: 'public/404.html', status: :not_found
  end
end

class ArticlesController < ApplicationController
  rescue_from ActiveRecord::RecordNotFound, with: :article_not_found

  def show
    @article = Article.find(params[:id])
  end

  private

  def article_not_found
    redirect_to articles_path, alert: 'Article not found.'
  end
end

class MyCustomError < StandardError; end

class ApplicationController < ActionController::Base
  rescue_from MyCustomError, with: :handle_custom_error

  private

  def handle_custom_error
    render file: 'public/500.html', status: :internal_server_error, layout: false
  end
end

class ArticlesController < ApplicationController
  def show
    raise MyCustomError, "Something went wrong!"
  end
end

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, ActiveRecord::RecordInvalid, with: :handle_record_error

  private

  def handle_record_error(exception)
    case exception
    when ActiveRecord::RecordNotFound
      render file: 'public/404.html', status: :not_found
    when ActiveRecord::RecordInvalid
      render file: 'public/422.html', status: :unprocessable_entity
    else
      render file: 'public/500.html', status: :internal_server_error
    end
  end
end

class ApplicationController < ActionController::Base
  rescue_from StandardError, with: :handle_standard_error

  private

  def handle_standard_error(exception)
    # エラーをログに記録
    logger.error "#{exception.class.name} (#{exception.message}):"
    logger.error exception.backtrace.join("\n")

    # エラー通知（例: Airbrake, Sentry）
    # Airbrake.notify(exception)

    render file: 'public/500.html', status: :internal_server_error, layout: false
  end
end

Rails.application.config.session_store :cookie_store, key: '_myapp_session'

# その他のオプション
Rails.application.config.session_store :cookie_store, key: '_myapp_session', expire_after: 1.hour, secure: true

class SessionsController < ApplicationController
  def create
    user = User.find_by(email: params[:email])

    if user&.authenticate(params[:password])
      session[:user_id] = user.id
      redirect_to root_url, notice: 'Logged in successfully!'
    else
      flash.now[:alert] = 'Invalid email or password'
      render :new
    end
  end

  def destroy
    session.delete(:user_id)
    redirect_to root_url, notice: 'Logged out successfully!'
  end
end

Rails.application.config.session_store :active_record_store, key: '_myapp_session'

class SessionsController < ApplicationController
  def create
    if login_successful?
      redirect_to root_path
    else
      redirect_to login_path, alert: 'Invalid credentials'
    end
  end
end

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    render :show  # app/views/users/show.html.erb をレンダリング
  end
end

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    redirect_to user_path(@user)  # users#show のパスを取得してリダイレクト
  end
end

class UsersController < ApplicationController
  def update
    @user = User.find(params[:id])
    if @user.update(user_params)
      redirect_to @user
    else
      render :edit
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :email)
  end
end

class UsersController < ApplicationController
  def index
    if request.xhr?  # AJAXリクエストかどうかを判定
      render json: User.all
    else
      @users = User.all
    end
  end
end

class UsersController < ApplicationController
  def destroy
    @user = User.find(params[:id])
    @user.destroy
    head :no_content  # HTTPステータスコード204を返す
  end
end

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    respond_to do |format|
      format.html  # app/views/users/show.html.erb をレンダリング
      format.json { render json: @user }
    end
  end
end

class SessionsController < ApplicationController
  def create
    user = User.find_by(email: params[:email])
    if user&.authenticate(params[:password])
      session[:user_id] = user.id
      redirect_to root_path
    else
      redirect_to login_path, alert: 'Invalid credentials'
    end
  end

  def destroy
    session.delete(:user_id)
    redirect_to root_path
  end
end

class UsersController < ApplicationController
  def index
    @users = Rails.cache.fetch('all_users', expires_in: 1.hour) do
      User.all
    end
  end
end

<% cache 'all_users' do %>
  <% @users.each do |user| %>
    <div>
      <%= user.name %>
    </div>
  <% end %>
<% end %>

class ProductsController < ApplicationController
  before_action :authenticate_user!, only: [:admin_dashboard]

  caches_page :index, :show

  def index
    @products = Product.all
  end

  def show
    @product = Product.find(params[:id])
  end

  def admin_dashboard
    @orders = Order.all
  end
end

class Product < ApplicationRecord
  def self.cached_products
    Rails.cache.fetch('cached_products', expires_in: 1.hour) do
      Product.all.to_a
    end
  end
end

class UsersController < ApplicationController
  def create
    @user = User.new(user_params)

    if @user.save
      Rails.cache.delete('all_users')  # キャッシュの削除
      redirect_to @user
    else
      render :new
    end
  end
end