I am trying to categorize something using Roman numerals from I to VI and use those to group_by in kanban and tree view. However sorting happens in alphabetical order.

I tried use a selection field, but the classification depicted by the Roman numeral is computed and needs to be assigned in python.

I tried storing the index of the list item, tuples and a dictionary but I cannot get it to work. I am not sure which value needs to be stored in the database to represent the correct selection.

I would also be open to different approaches.

RATING = [
            (1,'I'),
            (2,'II'),
            (3,'III'),
            (4,'IV'),
            (5,'V'),
            (6,'VI')
        ]

rating = fields.Selection( # Selection field?
        selection=RATING,
        compute='_compute_rating',
        store=True,
        string="Klasse"
    )


    @api.multi
    @api.depends('probability', 'impact')
    def _compute_rating(self):
        for risk in self:
            risk.probclass = risk.probability + risk.impact

            risk.risk_history = True

            if risk.probability == 50:
                risk.rating = 5
            elif risk.probclass in (31,42,41):
                risk.rating = 4
            elif risk.probclass in (21,32,43):
                risk.rating = 3
            elif risk.probclass in (11,22,33,44):
                risk.rating = 2
            elif risk.probclass in (12,23,34):
                risk.rating = 1
            elif risk.probclass in (14,13,24):
                risk.rating = 0