NHibernate + join to derived table - nhibernate

Question

In a table that stores multiple rows per employee, I want to pull one row per employee that represents the most recent entry for each employee. Here's where I am with hand-written SQL:
SELECT [all the selected columns here]
FROM Nominations t
inner join
(select max(NominationId) mostRecentNominationId,
EmployeeId from Nominations group by EmployeeId) n
on n.mostRecentNominationId = t_.NominationId
From source data like this:
nomination_id employee_id
-------------------------------
1 5
2 5
4 10
7 10
That'll give me something like this:
nomination_id employee_id
-------------------------------
2 5
7 10
I haven't been able to figure out how to accomplish that type of query via NHibernate ICriteria. Any thoughts?

Answer 1

Here is what you need to do:
DetachedCriteria dCriteria = DetachedCriteria.For<Nomination>("nomination")
.SetProjection(Projections.Max("nomination.Id"))
.Add(Restrictions.EqProperty("nomination.EmployeeId", "employee.Id"));
var nominations = Session.CreateCriteria<Nomination>("nom")
.CreateCriteria("Employee", "employee")
.Add(Subqueries.PropertyEq("nom.Id", dCriteria)).List<Nomination>();
This is not equilevant to the SQL query providfed in the question but it does exactly the same thing.
The SQL query that is generated by the above criteria query is:
SELECT *
FROM Nomination nom
inner join Employee employee on nom.EmployeeId=employee.EmployeeId
WHERE nom.NominationId =
(SELECT max(nomination.NominationId) as maxID
FROM Nomination nomination
WHERE nomination.EmployeeId = employee.EmployeeId)