docs: def get_instance(cls, instance_or_pk):
          """Return a model instance in ``db.session``.
  
          :param instance_or_pk: An instance of this model class, or a
            primary key. A composite primary key can be passed as a
            tuple.
  
          Example::
  
            @db.atomic
            def increase_account_balance(account, amount):
                # Here `Account` is a subclass of `db.Model`.
                account = Account.get_instance(account)
                account.balance += amount
  
            # Now `increase_account_balance` can be
            # called with an account instance:
            increase_account_balance(my_account, 100.00)
  
            # or with an account primary key (1234):
            increase_account_balance(1234, 100.00)
  
          """
  
          if isinstance(instance_or_pk, cls):
              if instance_or_pk in cls._flask_signalbus_sa.session:
                  return instance_or_pk
              instance_or_pk = inspect(cls).primary_key_from_instance(instance_or_pk)
          return cls.query.get(instance_or_pk)