この記事では、Railsのポリモーフィック関連付けを使ってコメント投稿機能を実装する際のポイントを紹介します。

1. バージョン情報

  • macOS：12.6
  • Ruby：3.1.2
  • Rails：6.1.6

2. 前提条件

  • Userモデル(ユーザー)
  • Bookモデル(本)のCRUD
  • Userモデルに紐づいたReportモデル(日報)のCRUD

3. 実装時のポイント

3-1. ポリモーフィック関連付け

BookモデルとReportモデルに従属するCommentモデルの作成

$ rails g model comment user:references commentable:references{polymorphic} content:text --no-test-framework

app/models/comment.rb

class Comment < ApplicationRecord
  belongs_to :user
  belongs_to :commentable, polymorphic: true

  validates :content, presence: true # 追記
end

db/migrate/XXXX_create_comments.rb

class CreateComments < ActiveRecord::Migration[6.1]
  def change
    create_table :comments do |t|
      t.references :user, null: false, foreign_key: true
      t.references :commentable, polymorphic: true, null: false
      t.text :content

      t.timestamps
    end
  end
end

マイグレーションを実行

$ rails db:migrate

db/schema.rb

  create_table "comments", force: :cascade do |t|
    t.integer "user_id", null: false
    t.string "commentable_type", null: false
    t.integer "commentable_id", null: false
    t.text "content"
    t.datetime "created_at", precision: 6, null: false
    t.datetime "updated_at", precision: 6, null: false
    t.index ["commentable_type", "commentable_id"], name: "index_comments_on_commentable"
    t.index ["user_id"], name: "index_comments_on_user_id"
  end
  • commentable_typeカラムにセットされるのは参照する親モデルのクラス名(BookまたはReport)

app/models/book.rb

class Book < ApplicationRecord
  has_many :comments, as: :commentable, dependent: :destroy # 追記
end

app/models/report.rb

class Report < ApplicationRecord
  belongs_to :user
  has_many :comments, as: :commentable, dependent: :destroy # 追記

  validates :title, presence: true
  validates :content, presence: true
end

3-2. コメント作成

ルーティングの設定

config/routes.rb

Rails.application.routes.draw do
  # 省略
  resources :books do
    resources :comments, only: :create, module: :books
  end
  resources :reports do
    resources :comments, only: :create, module: :reports
  end
end
HTTP verbPathController#ActionHelper
POST/books/:book_id/commentsbooks/comments#createbook_comments_path
POST/reports/:report_id/commentsreports/comments#createreport_comments_path

Commentsコントローラーの作成

$ rails g controller Comments --no-assets --no-helper --no-test-framework

app/controllers/comments_controller.rb

class CommentsController < ApplicationController
  def create
    @comment = @commentable.comments.build(comment_params)
    @comment.user = current_user
    if @comment.save
      redirect_to @commentable, notice: t('controllers.common.notice_create', name: Comment.model_name.human)
    else
      # コメント作成失敗時の処理は後述
    end
  end

  private

  def comment_params
    params.require(:comment).permit(:content)
  end
end

Books::Commentsコントローラーの作成

app/controllers/books/comments_controller.rb

class Books::CommentsController < CommentsController
  before_action :set_commentable

  private

  def set_commentable
    @commentable = Book.find(params[:book_id])
  end
end

Reports::Commentsコントローラーの作成

app/controllers/reports/comments_controller.rb

class Reports::CommentsController < CommentsController
  before_action :set_commentable

  private

  def set_commentable
    @commentable = Report.find(params[:report_id])
  end
end

コメント投稿フォームの作成

app/views/comments/_form.html.erb

<%= form_with model: [commentable, comment] do |f| %>
  <% if comment.errors.any? %>
    <div id="error_explanation">
      <h2>
        <%= I18n.t("errors.messages.not_saved",
                  count: comment.errors.count,
                  resource: comment.class.model_name.human.downcase) %>
      </h2>
      <ul>
        <% comment.errors.full_messages.each do |message| %>
          <li><%= message %></li>
        <% end %>
      </ul>
    </div>
  <% end %>

  <%= f.text_field :content, required: true %>
  <%= f.submit t('.create') %>
<% end %>
  • form_with model: [commentable, comment]

本と日報の詳細画面からコメントを投稿できるようにする

app/controllers/books_controller.rb

class BooksController < ApplicationController
  # 省略
  def show
    @comment = Comment.new
  end
end
  • フォームに渡す@commentを定義

app/controllers/reports_controller.rb

class ReportsController < ApplicationController
  # 省略
  def show
    @comment = Comment.new
  end
end
  • フォームに渡す@commentを定義

app/views/books/show.html.erb

<%= render 'comments/form', commentable: @book, comment: @comment %>
  • フォーム側でbook_comments_pathを生成

app/views/reports/show.html.erb

<%= render 'comments/form', commentable: @report, comment: @comment %>
  • フォーム側でreport_comments_pathを生成

i18nで日本語化

ja.yml

ja:
  activerecord:
    models:
      comment: コメント
  controllers:
    common:
      notice_create: "%{name}が作成されました。"
  comments:
    form:
      create: コメントする

3-3. コメント表示

コメント一覧パーシャルの作成

app/views/comments/_comments.html.erb

<div class="comments-container">
  <strong><%= Comment.model_name.human %>:</strong>
  <% if comments.any? %>
    <ul>
      <% comments.each do |comment| %>
        <% if comment.persisted? %>
          <li>
            <%= comment.content %>
            <small>
              (<%= link_to comment.user.name_or_email, comment.user %> - <%= l comment.created_at, format: :short %>)
            </small>
          </li>
        <% end %>
      <% end %>
    </ul>
  <% else %>
    (<%= t('.no_comments') %>)
  <% end %>
</div>

app/models/user.rb

class User < ApplicationRecord
  # 省略
  def name_or_email
    name.empty? ? email : name
  end
end
  • name_or_email
    • ユーザー名が入力されていればユーザー名を表示、未入力ならメールアドレスを表示

app/controllers/books_controller.rb

class BooksController < ApplicationController
  # 省略
  def show
    @comment = Comment.new
    @comments = @book.comments # 追記
  end
end
  • コメント一覧パーシャルに渡す@commentsを定義

app/controllers/reports_controller.rb

class ReportsController < ApplicationController
  # 省略
  def show
    @comment = Comment.new
    @comments = @report.comments # 追記
  end
end
  • コメント一覧パーシャルに渡す@commentsを定義

app/views/books/show.html.erb

<%= render 'comments/comments', comments: @comments %>

app/views/reports/show.html.erb

<%= render 'comments/comments', comments: @comments %>

i18nで日本語化

ja.yml

ja:
  activerecord:
    models:
      comment: コメント
  comments:
    comments:
      no_comments: コメントはまだありません

3-4. コメント作成失敗時の処理

コメント作成失敗時に本または日報の詳細画面に遷移する

app/controllers/comments_controller.rb

class CommentsController < ApplicationController
  def create
    @comment = @commentable.comments.build(comment_params)
    @comment.user = current_user
    if @comment.save
      redirect_to @commentable, notice: t('controllers.common.notice_create', name: Comment.model_name.human)
    else
      # コメント作成失敗時の処理を追記
      @comments = @commentable.comments
      render_commentable_show
    end
  end

  # 省略
end

app/controllers/books/comments_controller.rb

class Books::CommentsController < CommentsController
  before_action :set_commentable

  private

  # 省略

  def render_commentable_show
    @book = @commentable
    render 'books/show'
  end
end

app/controllers/reports/comments_controller.rb

class Reports::CommentsController < CommentsController
  before_action :set_commentable

  private

  # 省略

  def render_commentable_show
    @report = @commentable
    render 'reports/show'
  end
end

i18nで日本語化

ja.yml

ja:
  activerecord:
    models:
      comment: コメント
  controllers:
    common:
      notice_create: "%{name}が作成されました。"

3-5. コメント削除・編集

ルーティングの設定

config/routes.rb

Rails.application.routes.draw do
  # 省略
  resources :books do
    resources :comments, only: %i[create destroy edit update], module: :books
  end
  resources :reports do
    resources :comments, only: %i[create destroy edit update], module: :reports
  end
end
HTTP verbPathController#ActionHelper
POST/books/:book_id/commentsbooks/comments#createbook_comments_path
GET/books/:book_id/comments/:id/editbooks/comments#editedit_book_comment_path
PATCH/books/:book_id/comments/:idbooks/comments#updatebook_comment_path
DELETE/books/:book_id/comments/:idbooks/comments#destroybook_comment_path

edit・update・destroyアクションの追加

app/controllers/comments_controller.rb

class CommentsController < ApplicationController
  before_action :set_comment, only: %i[edit update destroy]

  def edit; end

  def create
    # 省略
  end

  def update
    if @comment.update(comment_params)
      redirect_to @commentable, notice: t('controllers.common.notice_update', name: Comment.model_name.human)
    else
      render :edit
    end
  end

  def destroy
    @comment.destroy

    redirect_to @commentable, notice: t('controllers.common.notice_destroy', name: Comment.model_name.human)
  end

  private

  def set_comment
    @comment = Comment.find(params[:id])
  end

  # 省略
end

コメント削除・編集リンクの追加

app/views/comments/_comments.html.erb

<div class="comments-container">
  <strong><%= Comment.model_name.human %>:</strong>
  <% if comments.any? %>
    <ul>
      <% comments.each do |comment| %>
        <% if comment.persisted? %>
          <li>
            <%= comment.content %>
            <small>
              (<%= link_to comment.user.name_or_email, comment.user %> - <%= l comment.created_at, format: :short %>)
            </small>
            <% if current_user == comment.user %>
              <%= link_to t('views.common.edit'), edit_polymorphic_path([commentable, comment]) %> |
              <%= link_to t('views.common.destroy'), polymorphic_path([commentable, comment]), method: :delete, data: { confirm: t('views.common.delete_confirm') } %>
            <% end %>
          </li>
        <% end %>
      <% end %>
    </ul>
  <% else %>
    (<%= t('.no_comments') %>)
  <% end %>
</div>
  • edit_polymorphic_path([commentable, comment])
    • "/books/1/comments/1/edit"または"/reports/1/comments/1/edit"
  • polymorphic_path([commentable, comment])
    • "/books/1/comments/1"または"/reports/1/comments/1"

app/views/books/show.html.erb

<%= render 'comments/comments', commentable: @book, comments: @comments %>
  • commentable: @bookを追記

app/views/reports/show.html.erb

<%= render 'comments/comments', commentable: @report, comments: @comments %>
  • commentable: @reportを追記

i18nで日本語化

ja.yml

ja:
  activerecord:
    models:
      comment: コメント
  views:
    common:
      edit: 編集
      destroy: 削除
      delete_confirm: よろしいですか？
  controllers:
    common:
      notice_update: "%{name}が更新されました。"
      notice_destroy: "%{name}が削除されました。"
  comments:
    comments:
      no_comments: コメントはまだありません