Linq-查询上一条下一条

//下一条
int pollid = poll.Where(f => f.PollID < CurrentId).OrderByDescending(o => o.PollID).FirstOrDefault().PollID;  

//上一条
int pollid = poll.Where(f => f.PollID > CurrentId).OrderByDescending(o => o.PollID).FirstOrDefault().PollID;