如何在Linq做一个简单的计数？

Question

我想做一个分页样式表,但是NeerDinner示例将整个数据提取到一个PaggingList类型中,并且我有超过10 000行要提取,所以我跳过了那一部分.

所以我想出了这个问题

var r = (from p in db.Prizes
            join c in db.Calendars on p.calendar_id equals c.calendar_id
            join ch in db.Challenges on c.calendar_id equals ch.calendar_id
            join ca in db.ChallengeAnswers on ch.challenge_id equals ca.challenge_id
            join cr in db.ChallengeResponses on ca.challenge_answer_id equals cr.challenge_answer_id

            where
                p.prize_id.Equals(prizeId)
                && ch.day >= p.from_day && ch.day <= p.to_day
                && ca.correct.Equals(true)
                && ch.day.Equals(day)

            orderby cr.Subscribers.name

            select new PossibleWinner()
            {
                Name = cr.Subscribers.name,
                Email = cr.Subscribers.email,
                SubscriberId = cr.subscriber_id,
                ChallengeDay = ch.day,
                Question = ch.question,
                Answer = ca.answer
            })
        .Skip(size * page)
        .Take(size);

问题是,如何在Take部件之前获得结果总数？

我在考虑:

var t = (from p in db.JK_Prizes
            join c in db.JK_Calendars on p.calendar_id equals c.calendar_id
            join ch in db.JK_Challenges on c.calendar_id equals ch.calendar_id
            join ca in db.JK_ChallengeAnswers on ch.challenge_id equals ca.challenge_id
            join cr in db.JK_ChallengeResponses on ca.challenge_answer_id equals cr.challenge_answer_id

            where
                p.prize_id.Equals(prizeId)
                && ch.day >= p.from_day && ch.day <= p.to_day
                && ca.correct.Equals(true)
                && ch.day.Equals(day)

            select cr.subscriber_id)
        .Count();

但那将再次进行查询......

有人建议我怎样才能有效地做到这一点？

Answer 1

如果你这样做一个查询:

var qry = (from x in y
           select x).Count();

... LINQ to SQL将足够聪明,使这成为一个SELECT COUNT查询,这可能相当有效(效率将更多地取决于查询中的条件).底线是计数操作发生在数据库中,而不是LINQ代码中.