class SaleOrderLine(models.Model): 
   _inherit = 'sale.order.line'

@api.multi
    @api.onchange('product_id')
    def product_id_change(self):
        res = super(SaleOrderLine, self).product_id_change()
      
        self.product_code=self.product_id.barcode
        self.product_code_details=self.product_id.product_code
        self.product_brand_line=self.product_id.brand
        self.price_unit=self.order_id.partner_id.cost*self.product_id.list_price#This is not updating
        print('RESSSSSSSSSS',self.price_unit)
        return res