account_invoice_calendar_event_eiru/calendar_event.py

# -*- coding: utf-8 -*-
# © 2016 Therp BV <http://therp.nl>
# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
from openerp import fields, models


class CalendarEvent(models.Model):
    _inherit = 'calendar.event'

    account_invoice_id = fields.Many2one('account.invoice', string='Referencia de Factura')