减法浮点字段odoo 9

Subtraction float field odoo 9

如何在函数中减去两个float字段"Finish - Start"

start = fields.Float(string='Star')
finish = fields.Float(string='Fin')
total = fields.Float(string='Total')

    @api.one
       def total_sum(self):
       ?????? 
def total_sum(self, cr, uid, ids, start, finish, context=None):
    res = {}
    res['total'] = finish - start
    return {'value': res}

应该是这样,

total = fields.Float(string='Total', compute=_set_total)

@api.multi
def _set_total(self):
    for rec in self:
        rec.total = float(rec.finish or 0.0) - float(rec.start or 0.0)

但是,您也可以创建该字段正常但不起作用

total = fields.Float(string='Total')

@api.onchange('finish','start')
def _set_total(self):
    self.total = float(self.finish or 0.00) - float(self.start or 0.00)