BiTemporal Data Modelをこんな感じで書きたいというネタ

bidm_interface.rb

class Employee
  include Foo::BitemporalModel

  # デフォルトにしたいなら、自分で書きたい
  # default_scope { btdm_valid }

  # findを上書きしたいなら、明示的に書きたい
  # alias find btdm_find
end

Employee.btdm_valid.to_sql
# => SELECT "employees".* FROM "employees" WHERE "employees"."valid_from" <= '2019-01-20 00:00:00' AND "employees"."valid_to" > '2019-01-20 00:00:00' AND "employees"."deleted_at" IS NULL

employee = Employee.btdm_find(1)
employee.id       #=> 1
employee.btdm_id  #=> 1

employee.update(name: 'a') #=> true
employee.id       #=> 2
employee.btdm_id  #=> 1

employee.update(name: 'b') #=> true
employee.id       #=> 3
employee.btdm_id  #=> 1

employee = Foo.travel_to(1.minute.ago) { Employee.btdm_find(1) }
employee.id        #=> 2
employee.foo_id    #=> 1
employee.readonly? #=> true