Linq-to-entities: Easy to find max value in SQL, but difficult in LINQ?

Question

I've started using Linq-to-entities with .NET 3.5, and I've come across a scenario that I can do real easy in SQL, but I'm having great difficulty with linq. I have a table in a SQL database with three fields, for purposes of this example I'll call them foo, bar, and foo_index and populate them like so:

Blockquote

foo | bar | foo_index

555 101 1

555 101 2

555 101 3

555 101 4

555 101 5

To get what bar is at the max foo_index where foo=555 the SQL is

---

SELECT bar, max(foo_index) as max_foo_index
FROM T
WHERE foo=555
GROUP BY bar

---

I've written some linq-to-entities code in C# that works, but I have a feeling there is a much more elegent solution out there, and that I'm missing some concept that would make the following much easier. Also, is there any way other then a foreach to get the data out of a var?

---

db_entity db = new db_entity();

var q =
     from table in db.T
     where table.FOO == 555
     select new { table.BAR, table.FOO_INDEX };

var q2 = 
     from t2 in q
     where t2.FOO_INDEX == table.Max(r => r.FOO_INDEX)
     select new { t2.BAR };

int result = 0;

foreach (var record in q2}
{
    result = record.BAR.Value;
}

---

Any help or guidance would be appreciated, Thanks!

Answer 1

I think this should work:

var query = from item in db.T
            where item.FOO == 555
            group item by item.BAR into g
            select new { Bar = g.Key, Max = g.Max(x => x.FOO_INDEX) };

So basically you're taking the same approach as in the SQL: group the data, then take the key for the group and the maximum FOO_INDEX within the group.

Answer 2

You can group elements in LINQ to Entities the same way you do in SQL. The syntax would look something like:

var q = from t in db.T
        where t.FOO == 555
        group t by t.BAR into g
        select new { 
                       Bar = group.Key, 
                       Max = g.Max(b => b.FOO_INDEX) 
                   };