Equivalent of outer join with non-equals predicate in Linq

Question

I am looking for the Linq-equivalent of the following SQL:

SELECT t0.Fk_CompanyId, t0.CheckedUtc, t0.IsBlocking
  FROM MyTable t0
  LEFT OUTER JOIN MyTable t1
    ON t0.Fk_CompanyId = t1.Fk_CompanyId AND t0.CheckedUtc < t1.CheckedUtc
 WHERE t1.Fk_CompanyId IS NULL
   AND t0.CheckedUtc IS NOT NULL

The closest I've got with Linq is:

from t0 in MyTable
join t1 in MyTable on t0.Fk_CompanyId equals t1.Fk_CompanyId into t1tmp
from t1 in t1tmp.DefaultIfEmpty()
where t1.Fk_CompanyId == null && t0.CheckedUtc != null && t0.CheckedUtc < t1.CheckedUtc
select new { cid = t0.Fk_CompanyId, cuct = t0.CheckedUtc, isbl = t0.IsBlocking }

... which produces the following SQL (reformatted slightly):

SELECT t0.Fk_CompanyId, t0.CheckedUtc, t0.IsBlocking
  FROM MyTable AS t0
  LEFT OUTER JOIN MyTable AS t1
    ON t0.Fk_CompanyId = t1.Fk_CompanyId
 WHERE (t1.Fk_CompanyId IS NULL)
   AND (t0.CheckedUtc IS NOT NULL)
   AND (t0.CheckedUtc < t1.CheckedUtc)

These are not exactly equivalent. (The t0.CheckedUtc < t1.CheckedUtc is pushed to the WHERE .) When I outer-left-join on t0.CheckedUtc < t1.CheckedUtc , this produces NULL values on the right-hand-side of the join. When I filter with WHERE instead, this removes all the NULL values that I am interested in.

Perspective: I am trying to find the rows in MyTable with the most recent CheckedUtc , if there are any non-NULL ones, grouped by Fk_CompanyId . And I want one row for each Fk_CompanyId . There are several "possible duplicates" that only deal with finding the most recent CheckedUtc s (but not their respective rows), or assume that CheckedUtc is NOT NULL.

So: How do I perform the equivalent of a join on a non-equals predicate in Linq?

Answer 1

Try this

from t0 in MyTable
From t1 in MyTable( x=>x.Fk_CompanyId=t0.Fk_CompanyId && x.CheckedUtc > t0.CheckedUtc ).DefaultIfEmpty()
where t1.Fk_CompanyId == null && t0.CheckedUtc != null 
select new { cid = t0.Fk_CompanyId, cuct = t0.CheckedUtc, isbl = t0.IsBlocking }