Question

I have a routine where I am accessing a table in the database and creating a model from the data.

Database Table TblUNote

      ID      Quarter      Year      SubID      Data
       1          1        2007       245      DataPoint1
       2          1        2007       245      Datapoint2
       3          1        2007       245      Datapoint3
       4          1        2007       247      DataPoint1
       5          1        2007       247      Datapoint2
       6          1        2007       247      Datapoint3
       7          1        2007       249      DataPoint1
       8          1        2007       249      Datapoint2

The routine is

       public RData[] GetData(int Q, int Y)
       {
          using (Entities be = new Entities())
          {
             List<RData> nlist = new List<RData>();

             List<TblUNote> info = be.TblUNotes.Where(a => a.Quarter == Q && a.Year == Y).ToList();
             foreach (var item in info)
             {
                 Rdata newmodel = new RData()
                 {
                    //create model
                 };
             }
             nlist.Add(newmodel);
          }
          return(nlist).ToArray();
       }

This works, but now I need to modify it so that only one model entry is created for each SubID. I have tried using .Distinct() but I just get the same data. I tried to use .First() but I keep getting an error no matter where I put it in the database call. I need the model list to have

               RData Model

     Item1    Quarter = 1,   Year = 2007,  SubID = 245,   Data = DataPoint1
     Item2    Quarter = 1,   Year = 2007,  SubID = 247,   Data = DataPoint1
     Item3    Quarter = 1,   Year = 2007,  SubID = 249,   Data = DataPoint1

The problem is I have nothing to compare SubID to. I thought .Distinct() would have given me a way to do this. I am sure that .First should but how do I integrate it into the database call.

Answer 1

You can use a GroupBy, and take first item of each group :

be.TblUNotes
  .Where(a => a.Quarter == Q && a.Year == Y)
  .GroupBy(m => m.SubId)
  .Select(g => g.FirstOrDefault())//or g.OrderBy(m => m.Data).FirstOrDefault(), for example, I don't know which item you wanna take
  .ToList();