Question

I am trying to find the most efficient way to get the most recent record in a joined table in LINQ.

This query may handle thousands of records so I didn’t want to perform a subquery.

I need everything from items, but only the most recent date from the “Notes” table, whose field name is SubmittedDate.

var items = (from t1 in db.Items
                         from t2
                            in db.Notes
                           .Where(o => (t1.Item_ID == o.Item_ID))
                         select new ItemModel
                         {
                             Name = t1.Name,
                             MostRecentUpdate = t2.SubmittedDate <== Need max value in model
                         });

Any help would be greatly appreciated.

Answer 1

It looks like you probably just want a group join:

var items = from t1 in db.Items
            join t2 in db.Notes on t1.Item_ID equals t2.Item_ID into notes
            select new ItemModel
            {
                Name = t1.Name,
                MostRecentUpdate = notes.Max(x => (DateTime?) x.SubmittedDate)
            };

Now MostRecentUpdate should be null if there are no non-null dates in the matching Notes rows. At least, that’s what the LINQ to Objects behaviour would be, so fingers crossed the abstraction holds…