https://joe11051105.gitbooks.io/you-need-to-know-about-ruby-on-rails/content/activerecord/persisted_vs_new_record.html

persisted? vs new_record?
Explain
  ● persisted? 判斷是否已經存入 database 且不是新增的資料
  ● new_record? 判斷是否是新增資料
Eaample
user = User.new

user.new_record?  # true
user.persisted?   # false

user = User.first

user.new_record?  # false
user.persisted?   # true