eiru_purchase_lines_total/models/purchase.py

# -*- coding: utf-8 -*-
##############################################################################
from openerp import tools, api
from openerp import api, fields, models, _

# class PickingTotalQty(models.Model):
#     _inherit = 'purchase.order'
#
#     tot_purchase_qty = fields.Float(compute='_calculate_purchase_qty', string='Total Cantidad Comprado', help="Total cantidad comprado")
#
#     def _calculate_purchase_qty(self):
#         for rs in self:
#             sumqty = 0
#             for line in rs.order_line:
#                 sumqty += line.product_qty
#         rs.tot_purchase_qty = sumqty

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

    tot_purchase_qty = fields.Float(string='Cantidad de Productos de Compra', compute='_calculate_purchase_qty')

    @api.depends('order_line.product_qty')
    def _calculate_purchase_qty(self):
        for order in self:
            order.tot_purchase_qty = sum(order.order_line.mapped('product_qty'))