expenses_of_products/models/account_invoice.py

# -*- encoding: utf-8 -*-
from openerp import models, fields, api, _
from openerp.exceptions import Warning

class account_invoice(models.Model):
    _inherit = 'account.invoice'

    product_id = fields.Many2one('product.product', 'Pieza Asociada al gasto')

    # @api.one
    # @api.onchange('invoice_line.product_id')
    # def update_product_account(self):
    #     if self.product_id:
    #         product = self.env['product.product'].browse([('id','=',self.product_id.id)])
    #         for each in self.invoice_line:
    #             each.account_id = product.property_account_expense.id
    #             self.env['account.invoice.line'].onchange_account_id(each.product_id, each.partner_id, self.type, self.fiscal_position, product.property_account_expense):