Question

How would the following sql query look when translated to linq?

SELECT     myId, Count(myId)  FROM MyTable  GROUP BY myId 

I’ve tried the following:

var q = from a in db.MyTable group a by a.Id into g let count = g.Count() select new {   Count = Id,   Key= g.Key }; 

but it raises an exception on enumeration indicating that there is no db function with a mapping named ‘Key’. I’m using LLBLGen on this particular app and I suspect that’s where the problem is rooted. I want to verify that my linq syntax is correct before I start digging though. Anyone see anything wrong?

Answer 1

Try this:

var q = from a in db.MyTable         group a by a.Id into g         select new { Id=g.Key, Count=g.Count() }; 

That’s nearly the same as yours, but your Count is obtained in a different way which looks wrong to me.

If LLBLGen doesn’t understand IGrouping.Key though, it could be tricky…

To check whether your LINQ syntax is correct or not, I’d recommend building a very simple in-memory list to use as your table. Here’s an example:

using System; using System.Collections.Generic; using System.Linq;  class Test {     static void Main()     {         var data = new[] {             new { Id='X', Name='Jon' },             new { Id='Y', Name='Marc' },             new { Id='X', Name='Holly' },         };          var query = from a in data                     group a by a.Id into g                     select new { Id=g.Key, Count=g.Count() };          foreach (var entry in query)         {             Console.WriteLine(entry);         }     } } 

This looks like it’s giving the right results to me.