public void CheckIfCanAddLineToOrder(SalesOrder order, SalesOrderLine line)
{
if (order.Lines.Count > 0)
{
throw new UserFriendlyException("订单明细太多了，不允许增加新的条目了");
}
}
public void AddLine(SalesOrderLine line, ISalesOrderPolicy salesOrderPolicy)
{
salesOrderPolicy.CheckIfCanAddLineToOrder(this, line);
this.Lines.Add(line);
}