expense_menu/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"

    is_a_expense = fields.Boolean(string="Es un gasto")

    @api.model
    def _get_default(self):
        x = self._context.get('is_a_expense')
        if x == True:
            return self.env['account.journal'].search([('code','=','GASTO')], limit=1)
        else:
            return super(account_invoice, self)._default_journal()

    _defaults = {
        'journal_id': _get_default
    }