Question

我从未在Linq之前使用过，而且真的没有时间学习。我的小知识不足以做到这一点，我需要你的帮助。这是我需要转换为Linq的代码。（我正在使用EF6和上下文）

WITH messages AS (
    SELECT s.siteId,s.originator,s.sentTime,s.mode,s.mainsFrequency,s.gensetFrequency,
            s.dgBattery,s.runHours,s.fuel,s.messageID,s.messageText,
           ROW_NUMBER() OVER(PARTITION BY s.originator 
                                 ORDER BY s.sentTime DESC) AS rk
      FROM smsParseds s)
SELECT m.*
FROM messages m
WHERE m.rk = 1
order by m.sentTime DESC

Answer 1

见Row_number over (Partition by xxx) in Linq? 做分区。

其余的是相当基本的linq语法。

我没有对此进行测试或尝试编译它，因此可能需要稍加修改。为了清楚起见，我将查询分解为类似于问题，但这些可以很容易地组合成一行。

var messages = smsParseds
   .OrderBy(o => o.sentTime).GroupBy(g => g.originator)
   .Select(s => new {s, rk = s.Count()})
   .SelectMany(sm => sm.s.Select(b => b)
      .Zip(Enumerable.Range(1,sm.rk), (j,i) => new {j.siteId, j.originator, j.sentTime, j.mode, j.mainsFrequency, j.gensetFrequency, j.dgBattery, j.runHours, j.fuel, j.messageID, j.messageText, rk = i}));

var result = messages
   .Where(w => w.rk = 1)
   .OrderByDescending(o => o.sentTime)

Answer 2

这不是直接翻译（实体框架不能使用行号），但结果应该是相同的

var query = from m in context.Messages
            where (from x in context.Messages
                   where m.Originator == x.Originator
                   where x.SentTime > m.SentTime
                   select x).Any() == false
            orderby m.SentTime desc
            select new
            {
              m.siteId,
              m.originator,
              m.sentTime,
              m.mode,
              m.mainsFrequency,
              m.gensetFrequency,
              m.dgBattery,
              m.runHours,
              m.fuel,
              m.messageID,
              m.messageText,
            };

需要帮助将T-Sql转换为Linq

2 个答案: