C# in Depth

312 CHAPTER 11 Query expressions and LINQ to Objectsvar tmp = from defect in SampleData.AllDefectswhere defect.AssignedTo != nullgroup defect by defect.AssignedTo;var query = from grouped in tmpselect new { Assignee=grouped.Key,Count=grouped.Count() };Of course, if you find this easier to read there’s nothing to stop you from breaking upthe original expression into this form in your source code. Nothing will be evaluateduntil you start trying to step through the query results anyway, due to deferred execution.Let’s extend this example to see how multiple continuations can be used. Ourresults are currently unordered—let’s change that so we can see who’s got the mostdefects assigned to them first. We could use a let clause after the first continuation,but listing 11.20 shows an alternative with a second continuation after our currentexpression.Listing 11.20Query expression continuations from group and selectvar query = from defect in SampleData.AllDefectswhere defect.AssignedTo != nullgroup defect by defect.AssignedTo into groupedselect new { Assignee=grouped.Key,Count=grouped.Count() } into resultorderby result.Count descendingselect result;foreach (var entry in query){Console.WriteLine("{0}: {1}",entry.Assignee.Name,entry.Count);}The changes between listing 11.19 and 11.20 are highlighted in bold. We haven’t hadto change any of the output code as we’ve got the same type of sequence—we’ve justapplied an ordering to it. This time the translated query expression is as follows:SampleData.AllDefects.Where (defect => defect.AssignedTo != null).GroupBy(defect => defect.AssignedTo).Select(grouped => new { Assignee=grouped.Key,Count=grouped.Count() }).OrderByDescending(result => result.Count);By pure coincidence, this is remarkably similar to the first defect tracking query wecame across, in section 10.3.5. Our final select clause effectively does nothing, so theC# compiler ignores it. It’s required in the query expression, however, as all queryexpressions have to end with either a select or a group … by clause. There’s nothingto stop you from using a different projection or performing other operations with thecontinued query—joins, further groupings, and so forth. Just keep an eye on the readabilityof the query expression as it grows.Licensed to Rhona Hadida