Question

Coming from Java, I am new to C# and LINQ. There are many queries in our code base which seem to not be optimally constructed. In the following query the GroupBy lambda expression creates an anonymous data type. I can’t find any examples online where GroupBy is used like this. Is there a way to simplify this query and still return the same results?

 List<MachineMetrics> machines = prod.Where(p => p.TimeProduced >= start &&
                                      p.TimeProduced <= end &&
                                      (jobID == -1 ? true : (p.JobID == jobID && p.Job.MachineID == MachineID))).
                                GroupBy(x => new
                                             {
                                                 MachineName = x.Job.Machine.MachineName,
                                                 MachineID = x.Job.MachineID,
                                                 JobName = x.Job.JobName,
                                                 JobID = x.JobID
                                              }).
                                Select(item => new MachineMetrics()
                                              {
                                                 MachineName = item.Key.MachineName,
                                                 MachineID = item.Key.MachineID,
                                                 JobName = item.Key.JobName,
                                                 JobID = item.Key.JobID
                                              }).
                                ToList<MachineMetrics>();

edit: Thanks for the help. The problem was the Equals() and GetHashCode() methods were not implimented for the class. Once I added those I used the code suggested by @Ladislav Mrnka and everything worked as expected.

Answer 1

You are looking for this:

List<MachineMetrics> machines = prod.Where(p => p.TimeProduced >= start &&
                                                p.TimeProduced <= end &&
                                                (jobID == -1 || 
                                                    (p.JobID == jobID && p.Job.MachineID == MachineID))).
                                    .Select(x => new MachineMetrics()
                                          {
                                             MachineName = x.Job.Machine.MachineName,
                                             MachineID = x.Job.MachineID,
                                             JobName = x.Job.JobName,
                                             JobID = x.JobID
                                          })
                                    .Distinct()
                                    .ToList();