Question

I have a basic LINQ Query that looks like the following:

var results = from x in context.MyEntities
              where (x.CustomerName != null)
              select new Customer()
              {
                CustomerID = x.CustomerID,
                FirstName = x.FirstName,
                LastName = x.LastName,
                Gender = x.Gender,
                BirthMonth = x.BirthMonth
              };

results = results.GroupBy(x => x.Gender);
results = results.GroupBy(x => x.BirthMonth);

bool onlyShowKnownGenders = GetWhetherToShowOnlySetGenders();
if (onlyShowKnownGenders) {
  results = results.Where(x => ((x.Gender == 1) || (x.Gender == 2)));
}

If I comment out the two “GroupBy” lines, my code works fine. However, I now have a need to group the results. When I include the two “GroupBy” lines, I receive an error that says:

Cannot implicitly convert type ‘System.Linq.IQueryable>’ to ‘System.Linq.IQueryable’. An explicit conversion exists (are you missing a cast?)

My question is, I’m not sure how to do the cast in this case. Can someone please help me out?

Thank you!

Answer 1

The problem is that after you call a group by you don’t get back an enumerable of (in this case) Customers. You get back an enumerable of groups.

A group of customers doesn’t have a BirthMonth property.

What exactly are you trying to do here?

Is this what you want?

var results1 = results.GroupBy(x => x.Gender);
var results2 = results1.Select(group => group.GroupBy(x => x.BirthMonth));

This would give you a group of groups at the end.
(I also incorporated dasblinkenlight’s answer in that you can’t re-use the same variable since the types are different).