【Rails】DM機能を実装する

1. 概要

• DeviseのUser同士でメッセージ（DM）を送受信
• 画面は 受信箱／送信済み／新規作成 の3つ

追加・編集するファイル

追加（新規）

• app/models/direct_message.rb
• db/migrate/*_create_direct_messages.rb
• app/controllers/direct_messages_controller.rb`
• app/views/direct_messages/index.html.erb
• app/views/direct_messages/new.html.erb

編集（追記）

• app/models/user.rb
• config/routes.rb

2. 生成コマンド

コマンドプロンプト

rails g controller direct_messages index new

rails g model DirectMessage sender:references recipient:references body:text

マイグレーションファイルを編集

db/migrate/*_create_direct_messages.rb

class CreateDirectMessages < ActiveRecord::Migration[7.0]
  def change
    create_table :direct_messages do |t|
      t.references :sender,    null: false, foreign_key: { to_table: :users }     # ← 修正
      t.references :recipient, null: false, foreign_key: { to_table: :users }     # ← 修正
      t.text :body, null: false
      t.timestamps
    end
    add_index :direct_messages, [:sender_id, :created_at]
    add_index :direct_messages, [:recipient_id, :created_at]
  end
end

コマンドプロンプト

rails db:migrate

3. models

app/models/direct_message.rb

class DirectMessage < ApplicationRecord
  belongs_to :sender,    class_name: "User"
  belongs_to :recipient, class_name: "User"

  validates :body, presence: true, length: { maximum: 10_000 }
  validate  :not_self

  scope :inbox_for,  ->(user_id) { where(recipient_id: user_id).order(created_at: :desc) }
  scope :outbox_for, ->(user_id) { where(sender_id:    user_id).order(created_at: :desc) }

  private
  def not_self
    errors.add(:base, "自分には送信できません") if sender_id.present? && sender_id == recipient_id
  end
end

app/models/user.rb

class User < ApplicationRecord
  # Devise モジュールは既存

  # ＝＝＝＝＝＝＝＝　ここから　＝＝＝＝＝＝＝＝
  has_many :sent_messages,     class_name: "DirectMessage",
                               foreign_key: :sender_id,
                               dependent: :destroy
  has_many :received_messages, class_name: "DirectMessage",
                               foreign_key: :recipient_id,
                               dependent: :destroy

  def display_name
    respond_to?(:name) && name.present? ? name : email
  end
  # ＝＝＝＝＝＝＝＝　ここまで　＝＝＝＝＝＝＝＝
end

4. routes

config/routes.rb

Rails.application.routes.draw do
  devise_for :users
  resources :posts

  resources :direct_messages, only: [:index, :new, :create] # 追加

  root "posts#index"
end

5. Controllers

app/controllers/direct_messages_controller.rb

class DirectMessagesController < ApplicationController
  before_action :authenticate_user!

  def index
    @inbox  = DirectMessage.inbox_for(current_user.id)
    @outbox = DirectMessage.outbox_for(current_user.id)
  end

  def new
    @message = DirectMessage.new(recipient_id: params[:recipient_id])
    @users   = User.where.not(id: current_user.id).order(created_at: :desc).limit(200)
  end

  def create
    @message = DirectMessage.new(message_params.merge(sender_id: current_user.id))
    if @message.save
      redirect_to direct_messages_path, notice: "送信しました"
    else
      @users = User.where.not(id: current_user.id).order(created_at: :desc).limit(200)
      render :new, status: :unprocessable_entity
    end
  end

  private
  def message_params
    params.require(:direct_message).permit(:recipient_id, :body)
  end
end

6. Views

DM一覧（受信箱／送信済み）

app/views/direct_messages/index.html.erb

<h1>DM</h1>

<h2>受信箱</h2>
<% if @inbox.blank? %>
  <p>受信メッセージはありません。</p>
<% else %>
  <ul>
    <% @inbox.each do |m| %>
      <li>
        <strong><%= m.sender.display_name %> ➜ あなた</strong><br>
        <%= simple_format(h(m.body)) %>
        <small><%= m.created_at.strftime("%Y-%m-%d %H:%M") %></small>
      </li>
    <% end %>
  </ul>
<% end %>

<h2>送信済み</h2>
<% if @outbox.blank? %>
  <p>送信メッセージはありません。</p>
<% else %>
  <ul>
    <% @outbox.each do |m| %>
      <li>
        <strong>あなた ➜ <%= m.recipient.display_name %></strong><br>
        <%= simple_format(h(m.body)) %>
        <small><%= m.created_at.strftime("%Y-%m-%d %H:%M") %></small>
      </li>
    <% end %>
  </ul>
<% end %>

<p><%= link_to "新規メッセージ", new_direct_message_path %></p>

DM一覧に行くためのリンク

app/views/layouts/application.html.erb

<li><%= link_to "DM", direct_messages_path %></li>

メッセージ新規作成

app/views/direct_messages/new.html.erb

<h1>新規メッセージ</h1>

<%= form_with model: @message, url: direct_messages_path, local: true do |f| %>
  <% if @message.recipient_id.present? %>
    <% recipient = User.find(@message.recipient_id) %>
    <p>宛先：<strong><%= recipient.display_name %></strong></p>
    <%= f.hidden_field :recipient_id %>  <!-- ★ 追加：選択済みを隠しで送る -->
  <% else %>
    <div class="field">
      <%= f.label :recipient_id, "宛先ユーザー" %><br>
      <%= f.collection_select :recipient_id, @users, :id, :display_name, include_blank: "選択してください" %>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :body, "本文" %><br>
    <%= f.text_area :body, cols: 50, rows: 5 %>
  </div>

  <%= f.submit "送信" %>
<% end %>

ユーザー詳細から「このユーザーにDM」

app/views/users/show.html.erb

<% if user_signed_in? && current_user.id != @user.id %>
  <p><%= link_to "このユーザーにDM", new_direct_message_path(recipient_id: @user.id) %></p>
<% end %>

投稿詳細から「作者にDM」

app/views/posts/show.html.erb

<% if user_signed_in? && @post.user && current_user.id != @post.user_id %>
  <p><%= link_to "作者にDM", new_direct_message_path(recipient_id: @post.user_id) %></p>
<% end %>