def prepare_relational_field_to_karat(instance, field):
    """ get data of instance at the end of relational field  
    """
    fields = field.split('__')
    field_data = instance
    for field in fields:
        if field == 'id':
            field_data = getattr(field_data, field, None)
            field_data = str(field_data).zfill(8)
        else:
            field_data = getattr(field_data, field, None)
    return field_data
