Select FROM Subquery without starting with another context object - entity-framework-core

Question

I am trying to model the following MSSQL query that I am trying to replicate in netCore 2.2 - EF Core:
SELECT
wonum,
MIN(requestdate) AS startdate,
MAX(requestdate) AS enddate,
MIN(laborcode)
FROM
(
SELECT
wo.wonum,
sw.requestdate,
wo.wolablnk AS 'laborcode'
FROM
DB1.dbo.web_users wu INNER JOIN
DB2.dbo.workorder wo on
wu.laborcode = wo.wolablnk INNER JOIN
DB2.dbo.sw_specialrequest sw on
wo.wonum = sw.wonum
WHERE
wo.status in ('LAPPR', 'APPR', 'REC') AND
sw.requestdate > GETDATE()
) a
GROUP BY
wonum
ORDER by
I have the subquery portion built and working but that leaves me at an impasse:
var workOrders = await _db1Context.Workorder
.Where(r => r.Status == "LAPPR" || r.Status == "APPR" || r.Status == "REC")
.ToListAsync();
var specialRequests = await _db2Context.SwSpecialRequest
.Where(r => r.Requestdate > DateTime.Now)
.ToListAsync();
var subQuery = (from webUser in webUsers
join workOrder in workOrders on webUser.Laborcode equals workOrder.Wolablnk
join specialRequest in specialRequests on workOrder.Wonum equals specialRequest.Wonum
orderby webUser.Laborcode, specialRequest.Requestdate, specialRequest.Wonum
select new { workOrder.Wonum, Laborcode = workOrder.Wolablnk, specialRequest.Requestdate, workOrder.Workorderid })
.ToList();
I am not sure how to initiate the query I need with the subquery i've built and i'm not sure if I am on the right track even. I've looked at a couple of other examples but i'm not getting it.
Would anyone be able to shed some light on the subject and help?
Thank you!

Answer 1

Write LINQ query identical to the SQL and do not mix with ToListAsync(). After ToListAsync() query is sent to the server. Also you should use only one DbContext for such query.
var webUsers = _db1Context.Webuser;
var workOrders = _db1Context.Workorder
.Where(r => r.Status == "LAPPR" || r.Status == "APPR" || r.Status == "REC");
var specialRequests = _db1Context.SwSpecialRequest
.Where(r => r.Requestdate > DateTime.Now);
var subQuery =
from webUser in webUsers
join workOrder in workOrders on webUser.Laborcode equals workOrder.Wolablnk
join specialRequest in specialRequests on workOrder.Wonum equals specialRequest.Wonum
select new
{
workOrder.Wonum,
Laborcode = workOrder.Wolablnk,
specialRequest.Requestdate
};
var resultQuery =
from a in subQuery
group a by a.Wonum into g
select new
{
Wonum = g.Key,
StartDate = g.Min(x => x.Requestdate),
EndDate = g.Max(x => x.Requestdate),
Laborcode = g.Min(x => x. Laborcode)
};
// final materialization
var result = await resultQuery.ToListAsync();