Purchase Order Global Discount

purchase_order_discount.py

from openerp import models, api
from openerp.osv import fields, osv
import openerp.addons.decimal_precision as dp


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

    def _get_order(self, cr, uid, ids, context=None):
        result = {}
        for line in self.pool.get('purchase.order.line').browse(cr, uid, ids, context=context):
            result[line.order_id.id] = True
        return result.keys()

    def _amount_all(self, cr, uid, ids, field_name, arg, context=None):
        res = {}
        cur_obj=self.pool.get('res.currency')
        line_obj = self.pool['purchase.order.line']
        for order in self.browse(cr, uid, ids, context=context):
            res[order.id] = {
                'amount_untaxed': 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
                line_price = line_obj._calc_line_base_price(cr, uid, line,
                                                            context=context)
                line_qty = line_obj._calc_line_quantity(cr, uid, line,
                                                        context=context)
                for c in self.pool['account.tax'].compute_all(
                        cr, uid, line.taxes_id, line_price, line_qty,
                        line.product_id, order.partner_id)['taxes']:
                    val += c.get('amount', 0.0)
            res[order.id]['amount_tax']=cur_obj.round(cr, uid, cur, val)
            if order.discount:
                res[order.id]['amount_untaxed']=cur_obj.round(cr, uid, cur, val1) * (1 - (order.discount or 0.0) / 100.0)
            else:
                res[order.id]['amount_untaxed']=cur_obj.round(cr, uid, cur, val1)
            res[order.id]['amount_total']=res[order.id]['amount_untaxed'] + res[order.id]['amount_tax']
        return res

    _columns = {
        'discount': fields.float(
            string='Discount (%)',
            digits_compute=dp.get_precision('Discount')
        ),
        'amount_untaxed': fields.function(
            _amount_all,
            digits_compute=dp.get_precision('Account'),
            string='Untaxed Amount',
            store={
              'purchase.order': (lambda s, c, u, i, x: i, ['discount'], 10),
              'purchase.order.line': (_get_order, None, 10),
            },
            multi="sums",
            help="The amount without tax",
            track_visibility='always'
        ),
        'amount_tax': fields.function(
            _amount_all, digits_compute=dp.get_precision('Account'), string='Taxes',
            store={
                'purchase.order': (lambda s, c, u, i, x: i, ['discount'], 10),
                'purchase.order.line': (_get_order, None, 10),
            },
            multi="sums",
            help="The tax amount"
        ),
        'amount_total': fields.function(
            _amount_all,
            digits_compute=dp.get_precision('Account'),
            string='Total',
            store={
                'purchase.order': (lambda s, c, u, i, x: i, ['discount'], 10),
                'purchase.order.line': (_get_order, None, 10),
            },
            multi="sums",
            help="The total amount"
        ),
    }

    _sql_constraints = [
        ('order_discount_limit', 'CHECK (discount <= 100.0)',
         'Discount must be lower than 100%.'),
    ]

purchase_order_discount.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
        <record id="purchase_order_discount" model="ir.ui.view">
            <field name="name">purchase.order.discount</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form" />
            <field name="arch" type="xml">
                <field name="date_order" position="after">
                    <field name="discount"/>
                </field>
            </field>
        </record>
    </data>
</openerp>