Filter on the selected enumerable in a linq query

Question

Is it possible to merge the below linq query into one query?

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 select new
                 {
                     RecordType = Type.GetType(x.Attributes["RecordType"]),
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

checkBoxes = from x in checkBoxes
             where x.RecordType != typeof(DomainModel.Group)
             select x;

Answer 1

var checkBoxes = from x in FindAll<CheckBox>()
                 let recordType = Type.GetType(x.Attributes["RecordType"])
                 where x.Checked && recordType != typeof(DomainModel.Group)
                 select new
                 {
                     RecordType = recordType,
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

Answer 2

var checkboxes = FindAll<CheckBox>()
                  .Where(x => x.Checked && Type.GetType(x.Attributes["RecordType"]) != typeof(DomainModel.Group))
                  .Select(new{
                          RecordType = Type.GetType(x.Attributes["RecordType"]),
                          RecordId = Int32.Parse(x.Attributes["RecordId"])
                  });

Answer 3

lasseespeholt's answer is perfectly good (preferable, even - there's no point in doing a projection if you're going to throw away the result), but if you want to apply this more generally, you can use a query continuation:

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 select new
                 {
                     RecordType = Type.GetType(x.Attributes["RecordType"]),
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 } into y
                 where y.RecordType != typeof(DomainModel.Group)
                 select y;

Here I've changed the second variable from x to y to make it clear that it's distinct from the original x, but you don't have to do that.

Another alternative which avoids calling Type.GetType twice but still putting the where clause before the final projection is to use a let clause (which introduces another projection itself, admittedly):

var checkBoxes = from x in FindAll<CheckBox>()
                 where x.Checked
                 let t = Type.GetType(x.Attributes["RecordType]")
                 where t != typeof(DomainModel.Group)
                 select new
                 {
                     RecordType = t
                     RecordId = Int32.Parse(x.Attributes["RecordId"])
                 };

Answer 4

Why would you want to change into one linq query? Linq uses deferred execution and will only execute when you actually use the output somewhere. In the mean time in keeps building up the expression tree. What you have is perfectly readable. I would only change it if you think it makes it more readable.