Question

I’m looking to fill an object model with the count of a linq-to-sql query that groups by its key.

The object model looks somewhat like this:

public class MyCountModel()
{
  int CountSomeByte1 { get; set; }
  int CountSomeByte2 { get; set; }
  int CountSomeByte3 { get; set; }
  int CountSomeByte4 { get; set; }
  int CountSomeByte5 { get; set; }
  int CountSomeByte6 { get; set; }
}

This is what I have for the query:

var TheQuery = from x in MyDC.TheTable
               where ListOfRecordIDs.Contains(x.RecordID) && x.SomeByte < 7
               group x by x.SomeByte into TheCount
               select new MyCountModel()
               {
                   CountSomeByte1 = TheCount.Where(TheCount => TheCount.Key == 1)
                                            .Select(TheCount).Count(),

                   CountSomeByte2 = TheCount.Where(TheCount => TheCount.Key == 2)
                                            .Select(TheCount).Count(),     
                   .....

                   CountSomeByte6 = TheCount.Where(TheCount => TheCount.Key == 6)
                                            .Select(TheCount).Count(), 

               }.Single();

ListOfRecordIDs is list of longs that’s passed in as a parameter. All the CountSomeByteN are underlined red. How do you do a count of grouped elements with the group’s key mapped to an object model?

Thanks for your suggestions.

Answer 1

The select is taking each element of your group and projecting them to identical newly created MyCountModels, and you’re only using one of them. Here’s how I’d do it:

var dict = MyDC.TheTable
    .Where(x => ListOfRecordIDs.Contains(x.RecordID) && x.SomeByte < 7)
    .GroupBy(x => x.SomeByte)
    .ToDictionary(grp => grp.Key, grp => grp.Count());

var result = new MyCountModel()
{
    CountSomeByte1 = dict[1];
    CountSomeByte2 = dict[2];
    CountSomeByte3 = dict[3];
    CountSomeByte4 = dict[4];
    CountSomeByte5 = dict[5];
    CountSomeByte6 = dict[6];
}

EDIT: Here’s one way to do it in one statement. It uses an extension method called Into, which basically works as x.Into(f) == f(x). In this context, it can be viewed as like a Select that works on the whole enumerable rather than on its members. I find it handy for eliminating temporary variables in this sort of situation, and if I were to write this in one statement, it’s probably how I’d do it:

public static U Into<T, U>(this T self, Func<T, U> func)
{
    return func(self);
}

var result = MyDC.TheTable
    .Where(x => ListOfRecordIDs.Contains(x.RecordID) && x.SomeByte < 7)
    .GroupBy(x => x.SomeByte)
    .ToDictionary(grp => grp.Key, grp => grp.Count())
    .Into(dict => new MyCountModel()
    {
        CountSomeByte1 = dict[1];
        CountSomeByte2 = dict[2];
        CountSomeByte3 = dict[3];
        CountSomeByte4 = dict[4];
        CountSomeByte5 = dict[5];
        CountSomeByte6 = dict[6];
    });