Hi,

I am trying to extend the sale.order class, but I do not know how to use the new field discount_rate in _amount_all.

Could someone help and clarify how to add this field?

This is the code to inherit the sale.order class adding the two new fields:
# -*- coding: utf-8 -*-
from openerp import models, fields, api
class SaleOrderDiscount(models.Model):
        _inherit = 'sale.order'
        discount_rate = fields.Float(
                string='Discount Rate (%)',
                readonly=False
        )
        amount_discount = fields.Float(
                string='Amount Discount'
        )
        @api.onchange('discount_rate', 'amount_untaxed')
        def calculate_discount(self):
                self.amount_discount = self.amount_untaxed * (self.discount_rate / 100)
        def _amount_all(self, cr, uid, ids, field_name, arg, context=None):
                cur_obj = self.pool.get('res.currency')
                res = {}
                for order in self.browse(cr, uid, ids, context=context):
                        res[order.id] = {
                                'amount_untaxed': 0.0,
                                'amount_discount': 0.0,
                                'amount_tax': 0.0,
                                'amount_total': 0.0,
                        }
                        val = val1 = 0.0
                        cur = order.pricelist_id.currency_id
                        for line in order.order_line:
                                val1 += line.price_subtotal
                                val += self._amount_line_tax(cr, uid, line, context=context)
                        val2 = val1 * (self.discount_rate / 100)
                        res[order.id]['amount_tax'] = cur_obj.round(cr, uid, cur, val)
                        res[order.id]['amount_untaxed'] = cur_obj.round(cr, uid, cur, val1)
                        res[order.id]['amount_discount'] = cur_obj.round(cr, uid, cur, val2)
                        res[order.id]['amount_total'] = res[order.id]['amount_untaxed'] + res[order.id]['amount_tax'] - res[order.id]['amount_discount']
                return res