[Rails]シンプル　ログイン機能実装　初心者

$ rails db:create #データベースすでにある方はこちら不要です

gem 'devise'

#deviseの導入
$ rails g devise:install

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

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

$ rails g devise user

$ rails db:migrate

#ログイン機能に必要なビューファイルを一切合切作ってくれます（ただし初期値のみ）
$ rails g devise:views

$ rails haml:erb2haml

%h2 Sign up
= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f|
  = render "devise/shared/error_messages", resource: resource
#ここから
  .field
    = f.label :nickname
    %br/
    = f.text_field :nickname
#ここまで追記
  .field
    = f.label :email
    %br/
    = f.email_field :email, autofocus: true, autocomplete: "email"
#以下略

class ApplicationController < ActionController::Base
  before_action :configure_permitted_parameters, if: :devise_controller?

  def configure_permitted_parameters
    devise_parameter_sanitizer.permit(:sign_up, keys: [:nickname]) # 新規登録時(sign_up時)にnicknameというキーのパラメーターを追加で許可する
  end
end