sale_product_line_limit/models/sale_order.py

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

class sale_order(models.Model):
    _inherit = 'sale.order'

    @api.multi
    def action_button_confirm(self):
        message1 = ""
        limite = 20
        if len(self.order_line) > limite:
            message1 += "La cantidad de Linea supera la cantidad permitida para la venta"
            message1 += "\n Cantidad Actual "+str(len(self.order_line))+" lineas"
            message1 += "\n Cantidad Permitida "+str(limite)+" lineas"

        if message1:
            raise Warning(_(message1.rstrip()))

        return super(sale_order,self).action_button_confirm()