Hi. I want to get line numbers in the purchase order. But it raises error regarding NewID when lines got changed. How it can be implemented ?

Doing it like this:

class PurchaseOrderLine(models.Model):
    _inherit = 'purchase.order.line'

    line_number = fields.Integer(string='#', default=1)


class PurchaseOrder(models.Model):
    _inherit = 'purchase.order'

    @api.onchange('order_line')
    def _compute_line_number(self):
        sorted_lines = sorted(self.order_line, key=lambda d: (d['sequence'], d['id']), reverse=False)
        cnt = 1
        for l in sorted_lines:
            l.line_number = cnt
            cnt += 1