Linq-to-entities: Easy to find max value in SQL, but difficult in LINQ?
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 开发者_开发百科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!
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.
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)
};
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