# ホームディレクリ直下のruby-campディレクトリに移動します。
$ cd ~/ruby-camp
​
# アプリ用のディレクトリ(今回はbook_shelf)を作成し、作成したディレクトリに移動する。
$ mkdir book_shelf
$ cd book_shelf

$ bundle init

# Gemfile
​
# frozen_string_literal: true
​
source "https://rubygems.org"
​
git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
​
- # gem "rails"
+ gem "rails", "5.2.1"

$ vi ~/.bashrc

alias bi='bundle install --path vendor/bundle --jobs=4'

$ source ~/.bash_profile

$ bi

$ bundle exec rails _5.2.1_ new .
# Gemfileがすでに存在するため、以下のメッセージが表示されるので、「y」を押した後にenterを押します。
       exist
      create  README.md
      create  Rakefile
      create  .ruby-version
      create  config.ru
      create  .gitignore
    conflict  Gemfile
Overwrite /Users/kazuma/ruby-camp/book_shelf/Gemfile? (enter "h" for help) [Ynaqdh]

# Gemfile
​
source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }
​
ruby '2.5.3'
​
# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
- gem 'rails', '~> 5.2.1'
+ gem 'rails', '5.2.1'
# Use sqlite3 as the database for Active Record
- gem 'sqlite3'
+ gem 'sqlite3', '~> 1.3.6'
# Use Puma as the app server
gem 'puma', '~> 3.11'
​
# 省略

$ bundle install

/vendor/bundle

$ echo "/vendor/bundle" >> .gitignore

$ vi ~/.bashrc

alias vbgi='echo "/vendor/bundle" >> .gitignore'

$ vbgi

$ bin/rails g resource book title:string price:integer publish_date:date description:text

# db/migrate/yyyyMMddHHmmss_create_books.rb
​
class CreateBooks < ActiveRecord::Migration[5.2]
  def change
    create_table :books do |t|
-     t.string :title
-     t.integer :price
-     t.date :publish_date
-     t.text :description
+     t.string :title, null: false, length: 50
+     t.integer :price, null: false
+     t.date :publish_date, null: false
+     t.text :description, null: false, length: 1000
      t.timestamps
    end
  end
end

$ bin/rails db:migrate

$ bin/rails db:migrate:status
​
database: /Users/kazuma/ruby-camp/book_shelf/db/development.sqlite3
​
 Status   Migration ID    Migration Name
--------------------------------------------------
   up     20181214071252  Create books

# Gemfile
​
# 省略
​
gem 'bootsnap', '>= 1.1.0', require: false
​
+ gem 'bootstrap', '~> 4.1.3'
+ gem 'jquery-rails'
​
group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end
​
group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end
​
# 省略

$ bi

// app/assets/javascripts/application.js
​
// 省略
​
//
//= require rails-ujs
//= require activestorage
//= require turbolinks
+ //= require jquery3
+ //= require popper
+ //= require bootstrap-sprockets
//= require_tree .

$ mv app/assets/stylesheets/application.css app/assets/stylesheets/application.scss

/* app/assets/stylesheets/application.scss */
​
/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
 * vendor/assets/stylesheets directory can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
 * files in this directory. Styles in this file should be added after the last require_* statement.
 * It is generally better to create a new file per style scope.
 *
-*= require_tree .
-*= require_self
 */
+@import "bootstrap";

$ mkdir app/views/shared
$ touch app/views/shared/_header.html.erb

# config/routes.rb
Rails.application.routes.draw do
  resources :books
+ root "books#index"
  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
end

<!-- app/views/shared/_header.html.erb -->
+ <nav class="navbar navbar-expand-lg navbar-dark bg-dark mb-3">
+   <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarToggler" aria-controls="navbarTogglerDemo03" aria-expanded="false" aria-label="Toggle navigation">
+     <span class="navbar-toggler-icon"></span>
+   </button>
+   <%= link_to "BookShelf", root_path, class: "navbar-brand" %>
+   <div class="collapse navbar-collapse" id="navbarToggler">
+     <ul class="navbar-nav mr-auto mt-2 mt-lg-0">
+       <li class="nav-item">
+         <%= link_to "Home", root_path, class: "nav-link" %>
+       </li>
+       <li class="nav-item">
+         <%= link_to "New Book", new_book_path, class: "nav-link" %>
+       </li>
+     </ul>
+     <form class="form-inline my-2 my-lg-0">
+       <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
+       <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
+     </form>
+   </div>
+ </nav>

<!-- application.html.erb -->
​
<!DOCTYPE html>
<html>
  <head>
    <title>BookShelf</title>
    <%= csrf_meta_tags %>
    <%= csp_meta_tag %>
​
    <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track': 'reload' %>
    <%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
  </head>
​
  <body>
+   <%= render "shared/header" %>
​
+   <div class="container">
+     <div class="row">
        <%= yield %>
+     </div>
+   </div>
  </body>
</html>

# app/controllers/books_controller.rb
​
class BooksController < ApplicationController
+ def index
+   @books = Book.all
+ end
end

$ touch app/views/books/index.html.erb

$ bin/rails s

# app/controllers/books_controller.rb
​
class BooksController < ApplicationController
  def index
    @books = Book.all
  end
​
+ def new
+   @book = Book.new
+ end
​
+ def create
+   @book = Book.new(book_params)
+   @book.save
+   redirect_to @book, notice: "書籍を登録しました。"
+ end
​
+ private
​
+ def book_params
+   params.require(:book).permit(:title, :price, :publish_date, :description)
+ end
end

# new.html.erbの作成
$ touch app/views/books/new.html.erb
​
# _form.html.erbの作成
$ touch app/views/books/_form.html.erb

<!-- app/views/books/new.html.erb -->
​
+ <div class="col-md-10 offset-md-1 mt-3">
+   <h2 class="text-center">書籍登録</h2>
+   <%= render 'form', book: @book %>
+ </div>

<!-- app/views/books/_form.html.erb -->
​
+ <%= form_with model: book, local: true do |form| %>
+   <div class="form-group">
+     <%= form.label :title %>
+     <%= form.text_field :title, class: "form-control" %>
+   </div>
+   <div class="form-group">
+     <%= form.label :price %>
+     <%= form.number_field :price, class: "form-control" %>
+   </div>
+   <div class="form-group">
+     <%= form.label :publish_date %>
+     <%= form.date_field :publish_date, class: "form-control" %>
+   </div>
+   <div class="form-group">
+     <%= form.label :description %>
+     <%= form.text_area :description, rows: 10, class: "form-control" %>
+   </div>
+   <%= form.submit class: "btn btn-primary" %>
+ <% end %>

# app/controllers/books_controller.rb
​
class BooksController < ApplicationController
  def index
    @books = Book.all
  end
​
  def new
    @book = Book.new
  end
​
  def create
    @book = Book.new(book_params)
    @book.save
    redirect_to @book, notice: "書籍を登録しました。"
  end
​
+ def show
+   @book = Book.find(params[:id])
+ end
​
  private
​
  def book_params
    params.require(:book).permit(:title, :price, :publish_date, :description)
  end
end

# show.html.erbの作成
$ touch app/views/books/show.html.erb
​
# _flash.html.erbの作成
$ touch app/views/shared/_flash.html.erb

<!-- app/views/books/show.html.erb -->
​
+ <div class="col-md-10 offset-md-1 mt-5">
+   <h2><%= @book.title %></h2>
+   <ul>
+     <li><b>価格: </b><%= number_with_delimiter @book.price %>円</li>
+     <li><b>発売日: </b><%= @book.publish_date %></li>
+   </ul>
+   <hr>
+   <h4>商品の説明</h4>
+   <%= simple_format @book.description %>
+ </div>

<!-- app/views/shared/_flash.html.erb -->
​
+ <% if flash.notice %>
+   <div class="alert alert-success" role="alert">
+     <%= flash.notice %>
+     <button type="button" class="close" data-dismiss="alert" aria-label="Close">
+       <span aria-hidden="true">&times;</span>
+     </button>
+   </div>
+ <% end %>
+ <% if flash.alert %>
+   <div class="alert alert-danger" role="alert">
+     <%= flash.alert %>
+     <button type="button" class="close" data-dismiss="alert" aria-label="Close">
+       <span aria-hidden="true">&times;</span>
+     </button>
+   </div>
+ <% end %>

<!-- app/views/layouts/application.html.erb -->
​
<!DOCTYPE html>
<html>
  <head>
    <title>BookShelf</title>
    <%= csrf_meta_tags %>
    <%= csp_meta_tag %>
​
    <%= stylesheet_link_tag    'application', media: 'all', 'data-turbolinks-track': 'reload' %>
    <%= javascript_include_tag 'application', 'data-turbolinks-track': 'reload' %>
  </head>
​
  <body>
    <%= render "shared/header" %>
    <div class="container">
+     <div class="row">
+       <div class="col-md-12">
+         <%= render "shared/flash" %>
+       </div>
+     </div>
      <div class="row">
        <%= yield %>
      </div>
    </div>
  </body>
</html>

# app/models/book.rb
​
class Book < ApplicationRecord
+ validates :title, presence: true, length: { maximum: 50 }
+ validates :price, presence: true,
+   numericality: { 
+     only_integer: true,
+     greater_than: 1
+   }
+ validates :publish_date, presence: true
+ validates :description, presence: true, length: { maximum: 1000 }
end

# app/controllers/books_controller.rb
​
class BooksController < ApplicationController
  def index
    @books = Book.all
  end
​
  def new
    @book = Book.new
  end
​
  def create
    @book = Book.new(book_params)
-   @book.save
-   redirect_to @book, notice: "書籍を登録しました。"
+   if @book.save
+     redirect_to @book, notice: "書籍を登録しました。"
+   else
+     render :new
+   end
  end
​
  def show
    @book = Book.find(params[:id])
  end
​
  private
​
  def book_params
    params.require(:book).permit(:title, :price, :publish_date, :description)
  end
end

$ touch app/views/shared/_errors.html.erb

<!-- app/views/books/_form.html.erb -->
​
<%= form_with model: book, local: true do |form| %>
+ <%= render "shared/errors", obj: book %>
  <div class="form-group">
    <%= form.label :title %>
    <%= form.text_field :title, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :new_image %>
    <%= form.file_field :new_image, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :price %>
    <%= form.number_field :price, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :publish_date %>
    <%= form.date_field :publish_date, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :description %>
    <%= form.text_area :description, rows: 10, class: "form-control" %>
  </div>
  <%= form.submit class: "btn btn-primary" %>
  <%= link_to '戻る', books_path, class: "btn btn-secondary" %>
<% end %>

<!-- app/views/shared/_errors.html.erb -->
​
+ <% if obj.errors.any? %>
+   <div class="alert alert-danger">
+     <p><b><%= obj.errors.count %>件のエラーがあります</b></p>
+     <ul>
+     <% obj.errors.full_messages.each do |message| %>
+       <li><%= message %></li>
+     <% end %>
+     </ul>
+   </div>
+ <% end %>

$ curl https://raw.githubusercontent.com/svenfuchs/rails-i18n/master/rails/locale/ja.yml -o config/locales/ja.yml

locales
│── en.yml
│── ja.yml
└── views
    └── books
        ├── en.yml
        └── ja.yml

# config/application.rb
​
require_relative 'boot'
​
require 'rails/all'
​
# Require the gems listed in Gemfile, including any gems
# you've limited to :test, :development, or :production.
Bundler.require(*Rails.groups)
​
module BookShelf
  class Application < Rails::Application
    # Initialize configuration defaults for originally generated Rails version.
    config.load_defaults 5.2
+   config.time_zone = 'Tokyo' # タイムゾーンもついでに変更
+   config.i18n.default_locale = :ja
+   config.i18n.load_path += Dir[Rails.root.join('config', 'locales', '**', '*.{rb,yml}').to_s]
    config.action_view.field_error_proc = Proc.new do |html_tag, instance|
      %Q(#{html_tag}).html_safe
    end
    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration can go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded after loading
    # the framework and any gems in your application.
  end
end

# config/locales/ja.yml
​
ja:
  activerecord:
+   models:
+     book: 書籍情報
+   attributes:
+     book:
+       title: タイトル
+       price: 価格
+       publish_date: 発売日
+       description: 詳細
    errors:
      messages:

$ mkdir -p config/locales/views/books/
$ touch config/locales/views/books/ja.yml

# config/locales/views/books/ja.yml
​
+ ja:
+   books:
+     new:
+       title: 書籍登録
+     show:
+       price: 価格
+       price_yen: "¥%{price}"
+       publish_date: 発売日
+       description: 商品の説明

<!-- app/views/books/new.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-3">
- <h2 class="text-center">書籍登録</h2>
+ <h2 class="text-center"><%= t '.title' %></h2>
  <%= render 'form', book: @book %>
</div>

<!-- app/views/books/show.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-5">
  <h2><%= @book.title %></h2>
  <ul>
-   <li><b>価格:</b><%= number_with_delimiter @book.price %>円</li>
-   <li><b>発売日:</b><%= @book.publish_date %></li>
+   <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
+   <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
  </ul>
  <hr>
- <h4>商品の説明</h4>
+ <h4><%= t ".description" %></h4>
  <%= simple_format @book.description %>
</div>

$ brew install imagemagick

# Gemfile
​
# -------- 省略 ----------
​
gem 'bootsnap', '>= 1.1.0', require: false
gem 'bootstrap', '~> 4.1.3'
gem 'jquery-rails'
+ gem 'mini_magick'
​
# -------- 省略 ----------

$ bi

$ bin/rails active_storage:install
$ bin/rails db:migrate

# app/models/book.rb
​
class Book < ApplicationRecord
+ has_one_attached :image
​
  validates :title, presence: true, length: { maximum: 50 }
  validates :price, presence: true,
    numericality: { 
      only_integer: true,
      greater_than: 1
    }
  validates :publish_date, presence: true
  validates :description, presence: true, length: { maximum: 1000 }
end

# app/controllers/books_controller.rb
​
class Book < ApplicationRecord
  has_one_attached :image
+ attribute :new_image
​
  validates :title, presence: true, length: { maximum: 50 }
  validates :price, presence: true,
    numericality: { 
      only_integer: true,
      greater_than: 1
    }
  validates :publish_date, presence: true
  validates :description, presence: true, length: { maximum: 1000 }
​
+ before_save do
+   self.image = new_image if new_image
+ end
end

<!-- app/views/books/_form.html.erb -->
​
<%= form_with model: book, local: true do |form| %>
  <%= render "shared/errors", obj: book %>
  <div class="form-group">
    <%= form.label :title %>
    <%= form.text_field :title, class: "form-control" %>
  </div>
+ <div class="form-group">
+   <%= form.label :new_image %>
+   <%= form.file_field :new_image, class: "form-control" %>
+ </div>
  <div class="form-group">
    <%= form.label :price %>
    <%= form.number_field :price, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :publish_date %>
    <%= form.date_field :publish_date, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :description %>
    <%= form.text_area :description, rows: 10, class: "form-control" %>
  </div>
  <%= form.submit class: "btn btn-primary" %>
<% end %>

# app/controllers/books_controller.rb
​
# 省略
​
  private
​
  def book_params
-   params.require(:book).permit(:title, :price, :publish_date, :description)
+   params.require(:book).permit(:title, :price, :publish_date,
+                                :description, :new_image)
  end

# config/locales/ja.yml
​
ja:
  activerecord:
    models:
      book: 書籍情報
    attributes:
      book:
        title: タイトル
        price: 価格
        publish_date: 発売日
        description: 詳細
+       new_image: 画像
+       image: 画像

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
    edit:
      title: 書籍更新
    show:
      price: 価格
      price_yen: "¥%{price}"
      publish_date: 発売日
      description: 商品の説明
+     edit: 編集
+     return: 戻る

$ curl http://spartacamp.jp/img/no_image.png -o ./app/assets/images/no_image.png

<!-- app/views/books/show.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-5">
- <h2><%= @book.title %></h2>
- <ul>
-   <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
-   <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
- </ul>
+ <div class="row">
+   <div class="col-md-4 mb-4">
+     <% if @book.image.attached? %>
+       <%= image_tag @book.image.variant(resize: "300x300"), class: "img-thumbnail" %>
+     <% else %>
+       <%= image_tag "no_image.png", class: "img-thumbnail" %>
+     <% end %>
+   </div>
+   <div class="col-md-8">
+     <h2><%= @book.title %></h2>
+     <ul>
+       <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
+       <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
+     </ul>
+   </div>
+ </div>
  <hr>
  <h4><%= t ".description" %></h4>
  <%= simple_format @book.description %>
+ <%= link_to t(".edit"), edit_book_path(@book), class: "btn btn-primary" %>
+ <%= link_to t(".return"), books_path, class: "btn btn-secondary" %>
</div>

# app/helpers/books_helper.rb
​
module BooksHelper
+ def show_book_image(book)
+   if book.image.attached?
+     image_tag book.image.variant(resize: "300x300"), class: "img-thumbnail"
+   else
+     image_tag "no_image.png", class: "img-thumbnail"
+   end
+ end
end

<!-- app/views/books/show.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-5">
  <div class="row">
    <div class="col-md-4 mb-4">
-     <% if @book.image.attached? %>
-       <%= image_tag @book.image.variant(resize: "300x300"), class: "img-thumbnail" %>
-     <% else %>
-       <%= image_tag "no_image.png", class: "img-thumbnail" %>
-     <% end %>
+     <%= show_book_image @book %>
    </div>
    <div class="col-md-8">
      <h2><%= @book.title %></h2>
      <ul>
        <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
        <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
      </ul>
    </div>
  </div>
  <hr>
  <h4><%= t ".description" %></h4>
  <%= simple_format @book.description %>
  <%= link_to t(".edit"), edit_book_path(@book), class: "btn btn-primary" %>
  <%= link_to t(".return"), books_path, class: "btn btn-secondary" %>
</div>

# app/controllers/books_controller.rb
​
# 省略
  def show
    @book = Book.find(params[:id])
  end
​
+ def edit
+   @book = Book.find(params[:id])
+ end
​
+ def update
+   @book = Book.find(params[:id])
+   if @book.update(book_params)
+     redirect_to @book, notice: "書籍を更新しました。"
+   else
+     render :edit
+   end
+ end
​
  private
​
  def book_params
    params.require(:book).permit(:title, :price, :publish_date,
                                 :description, :new_image)
  end
end

# edit.html.erbの作成
$ touch app/views/books/edit.html.erb

+ <div class="col-md-10 offset-md-1 mt-3">
+   <h2 class="text-center"><%= t '.title' %></h2>
+   <%= render 'form', book: @book %>
+ </div>

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
+   edit:
+     title: 書籍更新
    show:
      price: 価格
      price_yen: "¥%{price}"
      publish_date: 発売日
      description: 商品の説明
      edit: 編集
      return: 戻る

# app/controllers/books_controller.rb
​
# 省略
​
+ def destroy
+   @book = Book.find(params[:id])
+   @book.destroy
+   redirect_to books_path, notice: "書籍を削除しました。"
+ end
​
  private
​
  def book_params
    params.require(:book).permit(:title, :price, :publish_date,
                                 :description, :new_image)
  end
end

<!-- app/views/books/show.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-5">
  <div class="row">
    <div class="col-md-4 mb-4">
      <%= show_book_image @book %>
    </div>
    <div class="col-md-8">
      <h2><%= @book.title %></h2>
      <ul>
        <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
        <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
      </ul>
    </div>
  </div>
  <hr>
  <h4><%= t ".description" %></h4>
  <%= simple_format @book.description %>
  <%= link_to t(".edit"), edit_book_path(@book), class: "btn btn-primary" %>
+ <%= button_tag t(".delete"), class: "btn btn-warning", data: { toggle: "modal", target: "#delete-book" } %>
  <%= link_to t(".return"), books_path, class: "btn btn-secondary" %>
</div>
​
+ <div class="modal fade" id="delete-book">
+   <div class="modal-dialog">
+     <div class="modal-content">
+       <div class="modal-header">
+         <h5 class="modal-title" id="exampleModalLabel"><%= t(".modal_title") %></h5>
+         <button type="button" class="close" data-dismiss="modal" aria-label="Close">
+           <span aria-hidden="true">&times;</span>
+         </button>
+       </div>
+       <div class="modal-body">
+         <p><%= t(".question_book", book: @book.title) %></p>
+       </div>
+       <div class="modal-footer">
+         <button type="button" class="btn btn-secondary" data-dismiss="modal"><%= t(".chancel") %></button>
+         <%= link_to t(".delete_action"), book_path(@book), method: :delete, class: "btn btn-danger" %>
+       </div>
+     </div>
+   </div>
+ </div>

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
    edit:
      title: 書籍更新
    show:
      price: 価格
      price_yen: "¥%{price}"
      publish_date: 発売日
      description: 商品の説明
      edit: 編集
      return: 戻る
+     delete: 削除
+     modal_title: 書籍削除
+     question_book: "%{book}を削除しますか？"
+     delete_action: 削除する
+     chancel: キャンセル

+ <% @books.each do |book| %>
+   <div class="col-lg-3 col-md-4 col-sm-6 mb-3">
+     <%= show_book_image book %>
+     <h4 class="mt-2"><%= link_to book.title, book_path(book) %></h4>
+     <div><%= t(".price_yen", price: (number_with_delimiter book.price)) %></div>
+     <p><%= truncate(book.description, length: 20) %></p>
+   </div>
+ <% end %>

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
    edit:
      title: 書籍更新
    show:
      price: 価格
      price_yen: "¥%{price}"
      publish_date: 発売日
      description: 商品の説明
      edit: 編集
      return: 戻る
      delete: 削除
      modal_title: 書籍削除
      question_book: "%{book}を削除しますか？"
      delete_action: 削除する
      chancel: キャンセル
+   index:
+     price_yen: "¥%{price}"

# app/controllers/books_controller.rb
​
class BooksController < ApplicationController
+ before_action :set_book, only: [:show, :edit, :update, :destroy]
​
  def index
    @books = Book.all
  end
​
  def show
-   @book = Book.find(params[:id])
  end
​
  def new
    @book = Book.new
  end
​
  def create
    @book = Book.new(book_params)
    @book.save
    redirect_to @book, notice: "書籍を登録しました。"
  end
​
  def edit
-   @book = Book.find(params[:id])
  end
​
  def update
-   @book = Book.find(params[:id])
    @book.update(book_params)
    redirect_to @book, notice: "書籍を更新しました。"
  end
​
  def destroy
-   @book = Book.find(params[:id])
    @book.destroy
    redirect_to books_path, notice: "書籍を削除しました。"
  end
​
  private
​
  def book_params
    params.require(:book).permit(:name, :price, :publish, :publish_date)
  end
​
+ def set_book
+   @book = Book.find(params[:id])
+ end
​
end

$ bin/rails g model category name:string

$ bin/rails db:migrate

# db/seeds.rb
​
categories = %w(文学・評論 人文・思想 社会・政治･法律 ノンフィクション 歴史・地理 ビジネス 科学・テクノロジー 医学 コンピュータ・IT アート 趣味・実用 スポーツ・アウトドア 資格 暮らし 旅行ガイド コミック ライトノベル)
​
categories.each do |category|
  Category.create(name: category)
end

$ bin/rails db:seed

$ bin/rails g migration AddCategoriesIdToBooks category:references

# db/migrate/YYYYMMDDhhmmss_add_categories_id_to_books.rb
​
class AddCategoriesIdToBooks < ActiveRecord::Migration[5.2]
  def change
-   add_reference :books, :category, foreign_key: true
+   add_reference :books, :category, foreign_key: true, index: true, after: :description
  end
end

$ bin/rails db:migrate

# app/models/book.rb
​
class Book < ApplicationRecord
+ belongs_to :category
  has_one_attached :image
  attribute :new_image
​
# 以下省略

# app/models/category.rb
​
class Category < ApplicationRecord
+ has_many :books
end

<!-- app/views/books/_form.html.erb -->
​
<%= form_with model: book, local: true do |form| %>
  <%= render "shared/errors", obj: book %>
  <div class="form-group">
    <%= form.label :title %>
    <%= form.text_field :title, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :new_image %>
    <%= form.file_field :new_image, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :price %>
    <%= form.number_field :price, class: "form-control" %>
  </div>
  <div class="form-group">
    <%= form.label :publish_date %>
    <%= form.date_field :publish_date, class: "form-control" %>
  </div>
+ <div class="form-group">
+   <%= form.label :category_id %>
+   <%= form.collection_select :category_id, Category.all, :id, :name , { include_blank: t(".include_blank") },  { class: "form-control" } %>
+ </div>
  <div class="form-group">
    <%= form.label :description %>
    <%= form.text_area :description, rows: 10, class: "form-control" %>
  </div>
  <%= form.submit class: "btn btn-primary" %>
  <%= link_to '戻る', books_path, class: "btn btn-secondary" %>
<% end %>

# config/locales/ja.yml
​
ja:
  activerecord:
    models:
      book: 書籍情報
    attributes:
      book:
        title: タイトル
        price: 価格
        publish_date: 発売日
        description: 詳細
        new_image: 画像
+       category_id: カテゴリー
+       category: カテゴリー
    errors:

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
    edit:
      title: 書籍更新
+   form:
+     include_blank: カテゴリーを選択して下さい
    show:
      price: 価格

# app/controllers/books_controller.rb
​
# 省略
​
  private
​
  def book_params
    params.require(:book).permit(:title, :price, :publish_date,
-                                :description, :new_image)
+                                :description, :new_image, :category_id)
  end
​
  def set_book
    @book = Book.find(params[:id])
  end
end

<!-- app/views/books/show.html.erb -->
​
<div class="col-md-10 offset-md-1 mt-5">
  <div class="row">
    <div class="col-md-4 mb-4">
      <%= show_book_image @book %>
    </div>
    <div class="col-md-8">
      <h2><%= @book.title %></h2>
      <ul>
        <li><b><%= t ".price" %>: </b><%= t(".price_yen", price: (number_with_delimiter @book.price)) %></li>
        <li><b><%= t ".publish_date" %>: </b><%= @book.publish_date %></li>
+       <li><b><%= t ".category" %>: </b><%= @book.category&.name %></li>
      </ul>
    </div>
  </div>
​
<!-- 省略 -->

# config/locales/views/books/ja.yml
​
ja:
  books:
    new:
      title: 書籍登録
    edit:
      title: 書籍更新
    form:
      include_blank: カテゴリーを選択して下さい
    show:
      price: 価格
      price_yen: "¥%{price}"
      publish_date: 発売日
+     category: カテゴリー
      description: 商品の説明
      edit: 編集
      return: 戻る
      delete: 削除
      modal_title: 書籍削除
      question_book: "%{book}を削除しますか？"
      delete_action: 削除する
      chancel: キャンセル
    index:
      price_yen: "¥%{price}"

# Gemfile
​
# 省略
​
# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.1.0', require: false
gem 'bootstrap', '~> 4.1.3'
gem 'jquery-rails'
gem 'mini_magick'
+ gem 'devise'
​
group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
end
​
# 省略

$ bundle install
$ bin/rails g devise:install
​
# deviseをインストールした時に、deviseに関係するメッセージが表示されます。
===============================================================================
​
Some setup you must do manually if you haven't yet:
​
  1. Ensure you have defined default url options in your environments files. Here
     is an example of default_url_options appropriate for a development environment
     in config/environments/development.rb:
​
       config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }
​
     In production, :host should be set to the actual host of your application.
​
  2. Ensure you have defined root_url to *something* in your config/routes.rb.
     For example:
​
       root to: "home#index"
​
  3. Ensure you have flash messages in app/views/layouts/application.html.erb.
     For example:
​
       <p class="notice"><%= notice %></p>
       <p class="alert"><%= alert %></p>
​
  4. You can copy Devise views (for customization) to your app by running:
​
       rails g devise:views

#config/routes/rb
​
Rails.application.routes.draw do
  resources :books
  root "books#index"
  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
end

$ bin/rails g devise User nick_name:string

# db/migrate/XXXXXXXXXX_devise_create_users.rb
​
# frozen_string_literal: true
​
class DeviseCreateUsers < ActiveRecord::Migration[5.2]
  def change
    create_table :users do |t|
      ## Database authenticatable
      t.string :email,              null: false, default: ""
      t.string :encrypted_password, null: false, default: ""
​
      ## Recoverable
      t.string   :reset_password_token
      t.datetime :reset_password_sent_at
​
      ## Rememberable
      t.datetime :remember_created_at
​
      ## Trackable
      # t.integer  :sign_in_count, default: 0, null: false
      # t.datetime :current_sign_in_at
      # t.datetime :last_sign_in_at
      # t.string   :current_sign_in_ip
      # t.string   :last_sign_in_ip
​
      ## Confirmable
      # t.string   :confirmation_token
      # t.datetime :confirmed_at
      # t.datetime :confirmation_sent_at
      # t.string   :unconfirmed_email # Only if using reconfirmable
​
      ## Lockable
      # t.integer  :failed_attempts, default: 0, null: false # Only if lock strategy is :failed_attempts
      # t.string   :unlock_token # Only if unlock strategy is :email or :both
      # t.datetime :locked_at
​
      t.string :nick_name
​
      t.timestamps null: false
    end
​
    add_index :users, :email,                unique: true
    add_index :users, :reset_password_token, unique: true
    # add_index :users, :confirmation_token,   unique: true
    # add_index :users, :unlock_token,         unique: true
  end
end