【Rails】deviseを使ってログイン認証を実装する方法

gem 'devise'

Running via Spring preloader in process 27916
      create config/initializers/devise.rb
      create config/locales/devise.en.yml
===============================================================================

Depending on your application's configuration some manual setup may be required:

  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.

     * Required for all applications. *

  2. Ensure you have defined root_url to *something* in your config/routes.rb.
     For example:

       root to: "home#index"

     * Not required for API-only Applications *

  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>

     * Not required for API-only Applications *

  4. You can copy Devise views (for customization) to your app by running:

       rails g devise:views

     * Not required *

===============================================================================

まずURLの設定とアラート達の設置をしていきます。

<% if flash.notice %>
  <p class="notice"><%= notice %></p>
<% end %>
<% if flash.alert %>
  <p class="alert"><%= alert %></p>
<% end %>

Rails.application.routes.draw do
  devise_for :users
  devise_scope :user do#トップページをログイン画面に
    root "users/sessions#new"
  end
end

classApplicationController < ActionController::Base
  def after_sign_in_path_for(resource)
    "<ログイン後に遷移させたいページ>"
  end
end

gem 'devise-i18n'
gem 'devise-i18n-views'

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 Line
  class Application < Rails::Application
  # Initialize configuration defaults for originally generated Rails version.
    config.load_defaults 5.2
    config.i18n.default_locale = :ja