gistfile1.py

class Transaction(AppendOnlyModel):
    __tablename__ = 'transaction'
    __history_class__ = make_history_class(
        'transaction',
        status=HistoryStateColumn(
            sa.Enum(*constants.TRANSACTION_STATUSES),
            nullable=False)
    )

    source_id = ...
    destination_id = ...
    amount = ...
    currency = ...
                                                                                             
    status = append_only_attr('status', default_value='opened')