Entity Framework Correlated Sub-query

Question

I would like to create this using Entity Framework. A list of new objects containing fields from the parent and fields from the most current child record. I would write the SQL as a correlated sub-query:

SELECT p.PolicyNumber, p.HomeState, pt.RevisionDate, pt.TranStatus
FROM dbo.Policy p
JOIN dbo.PolicyTran pt ON p.Id = pt.Policy_Id
AND pt.RevisionDate = (
    SELECT MAX(mpt.RevisionDate)
    FROM dbo.PolicyTran mpt
    WHERE p.Id = pt.Policy_Id
    )
WHERE p.HomeState = 'NY'

The context for Policy has navigation to the list of transactions (PolicyTran).

var query = context.Policies.Include(t => t.PolicyTransactions);

No matter what I try the Linq is incorrect or the SQL is incorrect. Time to call in the experts.

Answer 1

It's not pretty but I believe this gets you what you wanted.

var query = db.Policies
.Where(p => p.HomeState == "NY")
.Join(db.PolicyTrans,
    p => p.Id,
    t => t.Policy_Id,
    (p, t) => new { P = p, T = t.OrderBy(tr => tr.RevisionDate).First() })
.Select(g => new {
    PolicyNumber = g.P.PolicyNumber,
    HomeState = g.P.HomeState,
    TransStatus = g.P.TransStatus,
    RevisionDate = g.T.RevisionDate
});

Answer 2

This is one way although 2 separate db hits. You could prob embed the first statement into the second one but that is more complicated for me right now as I don't have a compiler to hand.

var maxRevisionDate = context.PolicyTran.Max(x => x.RevisionDate);

var results = context.Policies.Where(x => x.PolicyTran.RevisionDate == maxRevisionDate 
               && x.HomeState == "NY").Include("PolicyTran")

I have made assumptions that your entity names are the SAME as your database tables. The result of this is an IEnumerable of Policies and their corresponding PolicyTrans.