Left joining a table's id with the maximum id from a subquery - linq

Question

I am using .NET core and trying to write a Linq query to list Cases. I have 3 tables that I am trying to join together:
Cases - Includes CaseID and CaseStatusID
CaseStatuses - Includes CaseStatusID (a Case has one of these)
CaseStatusHistory - Includes CaseStatusHistoryID, CaseID, CaseStatusID (a Case has many of these).
I can join Cases and CaseStatuses easily on CaseStatusID but am not sure how to join CaseStatusHistory on CaseStatusHistoryID = a subquery selecting the MAX(CaseStatusHistoryID) WHERE CaseID and CaseStatusID matches. I could even select the CaseStatusHitory later in my results but am not sure how.
This is what I need to convert
SELECT
c.CaseID,
csh.DateTimeAdded
FROM dbo.Cases c
JOIN dbo.CaseStatuses cs
ON c.CaseStatusID = cs.CaseStatusID
LEFT JOIN dbo.CaseStatusHistory csh
ON csh.CaseStatusHistoryID =
(
SELECT MAX(CaseStatusHistoryID)
FROM dbo.CaseStatusHistory
WHERE CaseID = c.CaseID
AND cs.CaseStatusID = c.CaseStatusID
)
This is what I have so far in Linq
IQueryable<CasesViewModel> objs =
from c in _db.Cases
from cs in _db.CaseStatuses.Where(cs => cs.CaseStatusId == c.CaseStatusId.Value).DefaultIfEmpty()
select new CasesViewModel
{
CaseID = c.CaseId,
CaseStatus = cs.CaseStatus
//StatusChangeDate = csh.DateTimeAdded
};
I need to add something like this
From csh In CaseStatusHistories
Where
(
From _csh In CaseStatusHistories
Where _csh.CaseID = c.CaseID AndAlso _csh.CaseStatusID = c.CaseStatusID
Select _csh.CaseStatusHistoryID
).Max = csh.CaseStatusHistoryID
Here is what I have so far but it does not return any result - just seems to time out.
IQueryable<CasesViewModel> objs =
from c in _db.Cases
from cs in _db.CaseStatuses.Where(cs => cs.CaseStatusId == c.CaseStatusId.Value).DefaultIfEmpty()
from rg in _db.RepairingGarages.Where(rg => rg.RepairingGarageId == c.RepairingGarageId.Value).DefaultIfEmpty()
from rgb in _db.Businesses.Where(rgb => rgb.BusinessId == rg.BusinessId.Value).DefaultIfEmpty()
from ec in _db.EngineeringCompanies.Where(ec => ec.EngineeringCompanyId == c.EngineeringCompanyId.Value).DefaultIfEmpty()
from ecb in _db.Businesses.Where(ecb => ecb.BusinessId == ec.BusinessId.Value).DefaultIfEmpty()
from csh in _db.CaseStatusHistory.Where(csh => csh.CaseStatusHistoryId ==
(
from _csh in _db.CaseStatusHistory
where _csh.CaseId == c.CaseId && _csh.CaseStatusId == c.CaseStatusId.Value
select _csh.CaseStatusHistoryId
).Max()).DefaultIfEmpty()
select new CasesViewModel
{
CaseID = c.CaseId,
RepairingGarage = rgb.BusinessName,
Engineer = ecb.BusinessName,
CaseStatus = cs.CaseStatus,
StatusChangeDate = csh.DateTimeAdded
};
I just need to get the StatusChangeDate which is the DateTimeAdded in the CaseStatusHistory table. Cases can be at the same status more than once, so I just need the DateTimeAdded with the highest CaseStatusHistoryID for a particular Case. Thank you very much for any help.

Answer 1

This appears to answer my question
IQueryable<CasesViewModel> objs =
from c in _db.Cases
from cs in _db.CaseStatuses.Where(cs => cs.CaseStatusId == c.CaseStatusId.Value).DefaultIfEmpty()
from rg in _db.RepairingGarages.Where(rg => rg.RepairingGarageId == c.RepairingGarageId.Value).DefaultIfEmpty()
from rgb in _db.Businesses.Where(rgb => rgb.BusinessId == rg.BusinessId.Value).DefaultIfEmpty()
from ec in _db.EngineeringCompanies.Where(ec => ec.EngineeringCompanyId == c.EngineeringCompanyId.Value).DefaultIfEmpty()
from ecb in _db.Businesses.Where(ecb => ecb.BusinessId == ec.BusinessId.Value).DefaultIfEmpty()
select new CasesViewModel
{
CaseID = c.CaseId,
RepairingGarage = rgb.BusinessName,
Engineer = ecb.BusinessName,
CaseStatus = cs.CaseStatus,
StatusChangeDate =
(
from _csh in _db.CaseStatusHistory
where _csh.CaseId == c.CaseId && _csh.CaseStatusId == cs.CaseStatusId
orderby _csh.CaseStatusHistoryId descending
select _csh.DateTimeAdded
).FirstOrDefault()
};
The only trouble with not joining is that I am not sure if I can sort by this date now. Any better ideas? Thank you.