使用左连接和组的Linq查询

Question

I'm unable to convert this SQL query into a working linq statement

select sum(cena), id_auta, max(servis) from dt_poruchy left outer join mt_auta on dt_poruchy.id_auta=mt_auta.id
where dt_poruchy.servis>=3 group by id_auta;

I tryed something like this but i cant handle the select statement

   var auta = from a in MtAuta.FindAll()
                   join p in DtPoruchy.FindAll() on a equals p.MtAuta into ap
                   from ap2 in ap.DefaultIfEmpty()
                   where ap2.SERVIS >= 3
                   group ap2 by ap2.ID into grouped
                   select new {

I'll appreciate any help!

Answer 1

Based on the limited information provided (which tables are certain fields from?), here is what I came up with.

var auta = from a in MtAuta.FindAll()
           let p = a.DtPoruchys.Where(s => s.SERVIS >= 3)
           select new
           {
               Id = a.Id,
               CenaSum = p.Sum(c => c.Cena),
               Servis = p.Max(s => s.SERVIS)
           };

Answer 2

I am not sure which table cena and servis are coming from but to create grouped sum you do something like.

select new { Sum = grouped.Sum( x => x.cena ) }

and to get max

select new { Max = grouped.Group.Max( x => x.servis ) }

Here is a good reference for you.

• MSDN - 101 LINQ Samples

Answer 3

I've reached this solution (supposing "cena" belongs to MtAuta.FindAll() ):

        var auta = from e in
                       (from a in DtPoruchy.FindAll()
                        where a.SERVIS >= 3
                        join p in MtAuta.FindAll() on a.MtAuta equals p.Id into ap
                        from ap2 in ap.DefaultIfEmpty()
                        select new
                        {
                            Cena = ap.cena,
                            IdAuta = a.MtAuta,
                            Servis = a.servis
                        })
                   group e by e.IdAuta into g
                   select new
                   {
                       Cena = g.Sum(e => e.cena),
                       IdAuta = g.Key,
                       Servis = g.Max(e => e.servis)
                   };

Answer 4

I've modified your solution little bit and i got it working like this:

var auta = from jo in
                       (
                           from a in MtAuta.FindAll()
                           join p in DtPoruchy.FindAll() on a equals p.MtAuta into ap
                           from ap2 in ap.DefaultIfEmpty()
                           where ap2.SERVIS >= 3
                           select new
                           {
                               Cena = ap2.CENA,
                               Idauto = ap2.ID_AUTA,
                               Servis = ap2.SERVIS
                           }
                       )
                   group jo by jo.Idauto into g
                   select new
                   {
                       Cena = g.Sum(jo => jo.Cena),
                       IdAuto = g.Key,
                       Servis = g.Max(jo => jo.Servis)
                   };

I just curious if this is the best solution?