@classmethod
def val(C, value):
    """return a string with a value ready for inclusion in SQL text."""
    if isinstance(value, str):
        return f"'{value}'"
    if value is None:
        return 'NULL'
    elif value is True:
        return 'TRUE'
    elif value is False:
        return 'FALSE'
    else:
        return f'{value}'
