Need help to convert T-Sql into Linq

Question

I have never used before Linq, and really have lack of time to study. My little knowledge is not enough to do this and I need your help. Here is a code which I need to convert into Linq. (I am using EF6 and context)

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

This is not a direct translation (Entity Framework cannot use Row Number), but the results should be the same

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,
            };

Answer 2

see Row_number over (Partition by xxx) in Linq? for doing the partition.

The rest is fairly basic linq syntax.

I haven't tested this or tried to compile it, so it may need a little modification. I split up the query similar to the question just for clarity, but these can easily be combined into one line.

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)