实体框架 - 将 SQL 查询转换为实体框架 Lambda 表达式

Question

I have this below query which I need to convert into a lambda expression:

select t.*
from (
   select DocId, max(Version) as maxversion
   from [DocumentVersion] group by DocId
) as x inner join [DocumentVersion] as t on f.DocId = x.docid and
       t.version = x.maxversion
where t.TestDocId =  12345

These are the column names = Id,DocSecId,Version, DocType, DocId, TestDocId, AppId, RppId, Regions, ExecutedDate EffectiveDate, Icheck, Vcheck, locked, Parentid, childId, LastCheckedId, Modified, Fresh

var dbData = db.DocumentVersion
    .Where(x => listofIds.Contains(x.DocTestId))
    .GroupBy(x => x.DocId).Select(
        g => new
        {
            DocId = g.Key,
            Version = g.Max(x => x.Version),
        })
    .ToList();

So far I have done the below query, but need to include all the columns in the output. In my case, I am getting two parameters as output - Count and Capacity:

Please help me with the code optimisation as well as the the output generation

Answer 1

As far as I see you have two tables with one to many relationships Document and DocumentVersion and you want to retrieve the latest/max version for the Documents with a given specific list of Ids . If this is the case with EF Core 6 you can use the new [MaxBy][1] method and do something like

var documentVersions = db.DocumentVersion
   .Where(x => listofIds.Contains(x.DocTestId))
   .GroupBy(x => x.DocId)
   .Select(g => g.MaxBy(x => x.Version))
   .ToList();

An implementation for EF Core 5 and the below version (including the original EF) prior to introducing the MaxBy operator will use the Max operator and will be something like

var documentVersions = db.DocumentVersion
   .Where(x => listofIds.Contains(x.DocTestId))
   .GroupBy(x => x.DocId)
   .Select(g => g.First(x => x.Version == g.Max(y =>  y.Version)))
   .ToList();