docs: def get_pk_values(cls, instance_or_pk):
          """Return a primary key as a tuple.
  
          :param instance_or_pk: An instance of this model class, or a
            primary key. A composite primary key can be passed as a
            tuple.
  
          """
  
          if isinstance(instance_or_pk, cls):
              cls._flask_signalbus_sa.session.flush()
              instance_or_pk = inspect(cls).primary_key_from_instance(instance_or_pk)
          return instance_or_pk if isinstance(instance_or_pk, tuple) else (instance_or_pk,)