odoo - Onchange method not saving -

so have onchange method looks it's working. when enter new value in onchange field triggers method writes value in field.

example code:

@api.onchange('xx_next_air_shipment') def _onchange_air_shipment(self):     self.xx_next_air_value = self.xx_next_air_shipment * self.xx_price_unit 

on screen looks correct, when press save value seem lost?

i tried editing write method, debugged , saw correct values in parameter returned write method correct values still didn't save database:

@api.one def write(self, vals):     openerp.pydev import pydevd     return self.write(vals) 

update method code,

@api.multi def write(self, vals):     openerp.pydev import pydevd     return super(class_name,self).write(vals) 

@daniel reis right method's result turns infinite loop.