text: import uuid
  import datetime
  from pony import orm
  
  db = orm.core.Database()
  
  
  class Users(db.Entity):
      id = orm.core.PrimaryKey(int, auto=True)
      uuid = orm.core.Optional(uuid.UUID, default=uuid.uuid4)
      username = orm.core.Required(str)
      token = orm.core.Optional(str)
      access_token = orm.core.Optional(str)
      refresh_token = orm.core.Optional(str)
      expiry = orm.core.Optional(datetime.datetime)
  
  
  class Employee(db.Entity):
      id = orm.core.PrimaryKey(int, auto=True)
      uuid = orm.core.Optional(uuid.UUID, default=uuid.uuid4)
      given_name = orm.core.Required(str)
      family_name = orm.core.Required(str)
      email = orm.core.Required(str, unique=True)
      manager = orm.core.Optional("Employee", reverse="manager")
      role = orm.core.Optional(str)
  
  