product_ean13_sale/sale_order_ean13.py

from openerp import models,api,fields

class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'
    _name = 'sale.order.line'

    ean13 = fields.Char(string="Codigo de Barras", compute="_get_ean13")

    @api.one
    @api.depends('product_id')
    def _get_ean13(self):
        self.ean13 = self.product_id.ean13