0. 前提

deviseが導入済み
devise trackableを導入済み

1. カラムの追加

今回はusers tableとします
current_sign_in_ip, にならい、current_とlast_と2つ作成します

add_column :users, :current_sign_in_user_agent, :string
add_column :users, :last_sign_in_user_agent, :string

2. config/initializers/devise.rbに追加

ファイル作ってもいんですけど、今回はdeviseを設定した直後にします

Devise.setup do |config|
  # ~~~
end

module DeviseExt
  module Models
    module Trackable
      def self.required_fields(klass)
        super + [ :current_sign_in_user_agent, :last_sign_in_user_agent ]
      end

      def update_tracked_fields(request)
        super
        old_current, new_current = self.current_sign_in_user_agent, extract_user_agent_from(request)
        self.last_sign_in_user_agent = old_current || new_current
        self.current_sign_in_user_agent = new_current
      end

      protected

      def extract_user_agent_from(request)
        request.user_agent
      end
    end
  end
end

Devise::Models::Trackable.prepend DeviseExt::Models::Trackable

3. 動作確認

Started POST "/users/sign_in" for ::1 at 2024-12-26 14:04:44 +0900
Processing by Devise::SessionsController#create as HTML
  Parameters: {"authenticity_token"=>"[FILTERED]", "user"=>{"email"=>"[FILTERED]", "password"=>"[FILTERED]", "remember_me"=>"0"}, "commit"=>"Log in"}
  User Load (1.4ms)  SELECT "users".* FROM "users" WHERE "users"."email" = 'test@example.com' ORDER BY "users"."id" ASC LIMIT 1 /*action='create',application='OidcServer',controller='sessions'*/
  TRANSACTION (0.2ms)  BEGIN /*action='create',application='OidcServer',controller='sessions'*/
  User Update (1.6ms)  UPDATE "users" SET "sign_in_count" = 2, "current_sign_in_at" = '2024-12-26 05:04:44.812636', "current_sign_in_user_agent" = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36', "last_sign_in_user_agent" = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36', "updated_at" = '2024-12-26 05:04:44.812949' WHERE "users"."id" = 1 /*action='create',application='OidcServer',controller='sessions'*/
  TRANSACTION (1.4ms)  COMMIT /*action='create',application='OidcServer',controller='sessions'*/
Redirected to http://localhost:3000/
Completed 303 See Other in 302ms (ActiveRecord: 4.5ms (2 queries, 0 cached) | GC: 6.1ms)