Linq join and group by - linq

Question

I am trying to write the following PLSQL query in linq, but am coming a little unstuck on the group by:
select
sub.EmpID,
Min(sub.Stage1) Stage1,
Min(sub.Stage2) Stage2,
Min(sub.Stage3) Stage3,
Min(sub.Prob1) Prob1,
Min(sub.Prob2) Prob2
from
(select
det.det_numbera EmpID,
case when apr.apr_performa = '1'
then max(apr.apr_datec)
else null
end Stage1,
case when apr.apr_performa = '2'
then max(apr.apr_datec)
else null
end Stage2,
case when apr.apr_performa = '3'
then max(apr.apr_datec)
else null
end Stage3,
case when apr.apr_performa = '5'
then max(apr.apr_datec)
else null
end Prob1,
case when apr.apr_performa = '6'
then max(apr.apr_datec)
else null
end Prob2
from emdet det
left outer join emapr apr
on det.det_numbera = apr.det_numbera
group by det.det_numbera, apr.apr_performa) sub
group by sub.Empid
I have managed to partially do the sub query but came unstuck on the grouping before I could get the outer query working:
public List<ComplianceDetails> MyComplianceDetails(List<JobDetail> staff, List<Compliance> compliance)
{
List<ComplianceDetails> compdet =
(from s in staff
join c in compliance on s.EmpID equals c.EmpId into staffcomp
from sc in staffcomp.DefaultIfEmpty()
group s by new { s.EmpID, sc.Stage } into grp
select new ComplianceDetails(
s.EmpID,
s.Position,
s.Department,
s.Division,
s.Contract,
s.ContService,
s.Probation,
s.Sessional,
s.Teaching,
sc.Stage == "1" ? staffcomp.Max(a => a.LastDate) : (DateTime?)null,
sc.Stage == "2" ? staffcomp.Max(a => a.LastDate) : (DateTime?)null,
sc.Stage == "3" ? staffcomp.Max(a => a.LastDate) : (DateTime?)null,
sc.Stage == "5" ? staffcomp.Max(a => a.LastDate) : (DateTime?)null,
sc.Stage == "6" ? staffcomp.Max(a => a.LastDate) : (DateTime?)null
)
).ToList();
return compdet;
}
EDIT//
Thanks for the help, you guided me very close to the solution this seems to work as expected:
public List<ComplianceDetails> MyComplianceDetails(List<JobDetail> staff, List<Compliance> compliance)
{
string[] tQuals = new string[] { "21", "22", "23", "24" };
var compdet =
(from det in staff
join apr in compliance on det.EmpID equals apr.EmpId
into JoinedList
from apr in JoinedList.DefaultIfEmpty()
group new { det, apr } by
new
{
det.EmpID,
Stage = apr == null ? "" : apr.Stage
} into GroupedList
select GroupedList.Select(u => new
{
EmpID = u.det.EmpID,
FullName = u.det.FullName,
Position = u.det.Position,
Department = u.det.Department,
Division = u.det.Division,
Contract = u.det.Contract,
ContService = u.det.ContService,
Probation = u.det.Probation,
Sessional = u.det.Sessional,
Teaching = u.det.Teaching,
Stage1 = u.apr == null ? null : (u.apr.Stage == "1" ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null),
Stage2 = u.apr == null ? null : (u.apr.Stage == "2" ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null),
Stage3 = u.apr == null ? null : (u.apr.Stage == "3" ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null),
Prob1 = u.apr == null ? null : (u.apr.Stage == "5" ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null),
Prob2 = u.apr == null ? null : (u.apr.Stage == "6" ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null),
EduType = u.apr == null ? string.Empty : (tQuals.Contains(u.apr.Stage) ? u.apr.StageDesc : string.Empty),
EduDate = u.apr == null ? null : (tQuals.Contains(u.apr.Stage) ? GroupedList.Max(t => t.apr.LastDate) : (DateTime?)null)
})
)
.SelectMany(u => u)
.GroupBy(u => u.EmpID)
.Select(u => new ComplianceDetails
(
u.Key,
u.First().FullName,
u.First().Position,
u.First().Department,
u.First().Division,
u.First().Contract,
u.First().ContService,
u.First().Probation,
u.First().Sessional,
u.First().Teaching,
u.Where(t => t.Stage1 == u.Max(T => T.Stage1)).Select(g => g.Stage1).FirstOrDefault(),
u.Where(t => t.Stage2 == u.Max(T => T.Stage2)).Select(g => g.Stage2).FirstOrDefault(),
u.Where(t => t.Stage3 == u.Max(T => T.Stage3)).Select(g => g.Stage3).FirstOrDefault(),
u.Where(t => t.Prob1 == u.Max(T => T.Prob1)).Select(g => g.Prob1).FirstOrDefault(),
u.Where(t => t.Prob2 == u.Max(T => T.Prob2)).Select(g => g.Prob2).FirstOrDefault(),
u.Where(t => t.EduDate == u.Max(T => T.EduDate)).Select(g => g.EduType).FirstOrDefault(),
u.Where(t => t.EduDate == u.Max(T => T.EduDate)).Select(g => g.EduDate).FirstOrDefault()
))
.ToList();
return compdet;
}

Answer 1

this is equivalent linq of your tsql, check this:
var query = (from det in emdet
join apr in emapr on det.det_numbera equals apr.det_numbera
into JoinedList
from apr in JoinedList.DefaultIfEmpty()
group new { det, apr } by
new
{
det.det_numbera,
apr_performa = apr == null ? "" : apr.apr.apr_performa
} into GroupedList
select GroupedList.Select(u => new
{
EmpID = u.det.det_numbera,
Stage1 = u.apr == null ? null : (u.apr.apr_performa == "1" ? GroupedList.Max(t => t.apr_datec) : null),
Stage2 = u.apr == null ? null : (u.apr.apr_performa == "2" ? GroupedList.Max(t => t.apr_datec) : null),
Stage3 = u.apr == null ? null : (u.apr.apr_performa == "3" ? GroupedList.Max(t => t.apr_datec) : null),
Prob1 = u.apr == null ? null : (u.apr.apr_performa == "5" ? GroupedList.Max(t => t.apr_datec) : null),
Prob2 = u.apr == null ? null : (u.apr.apr_performa == "6" ? GroupedList.Max(t => t.apr_datec) : null)
})
)
.SelectMany(u => u)
.GroupBy(u => u.EmpID)
.Select(u => new
{
EmpID = u.Key,
Stage1 = u.Where(t => t.Stage1 != null).DefaultIfEmpty().Min(t => t.Stage1),
Stage2 = u.Where(t => t.Stage2 != null).DefaultIfEmpty().Min(t => t.Stage2),
Stage3 = u.Where(t => t.Stage3 != null).DefaultIfEmpty().Min(t => t.Stage3),
Prob1 = u.Where(t => t.Prob1 != null).DefaultIfEmpty().Min(t => t.Prob1),
Prob2 = u.Where(t => t.Prob2 != null).DefaultIfEmpty().Min(t => t.Prob2)
})
.ToList();