Tuples In C#, A Useful Example


Last year I worked consulted with a company that had an engineer that used tuples in C# and tried to explain to me how they were useful.  To be honest, I never quite saw the value proposition (until today).  I remember he kept saying they were kind of like key value pairs but could go beyond that.  I remember those words but never internalized that.

The Example

My example is a simple one.  I’m currently working on providing data to an external application that will provide business intelligence (help with session selection) to the Silicon Valley Code Camp web site.  The data I’m providing is every mark of interest and plan to attend for every session ever given at code camp (that’s 220,000 records).  I also want to add to those records the session evaluation results for those people.  For example, one of those 220,000 records looks like this:

public class SessionAttendeeRec
    public string Id { get; set; } // because ST sends up strings on new records
    public int AttendeeId { get; set; }
    public int SessionId { get; set; }
    public bool Interested { get; set; }
    public bool WillAttend { get; set; }
    public DateTime LastUpdatedDate { get; set; }
    public int HoveredOverCount { get; set; }
    public bool EvalDone { get; set; }
    public int EvalCourseAsWhole { get; set; }
    public int EvalOverallCodeCamp { get; set; }

I can get most of this data from one table (SessionAttendee) which is defined as follows:

CREATE TABLE [dbo].[SessionAttendee] (
  [Id] int IDENTITY(1, 1) NOT NULL,
  [SessionsId] int NOT NULL,
  [AttendeesId] intNOT NULL,
  [Interestlevel] int NOT NULL,
  [LastUpdatedDate] datetime NULL,
  [UpdateByProgram] nvarchar(64) NULL,
  [Cnt] int NULL,
  [SignupDate] datetime NULL,
  [SignUpCancelByDate] datetime NULL,
  [PayDate] datetime NULL,
  [PayAmount] decimal(19, 4) NULL,
  [PayComment] varchar(1024)  NULL,
  [Note] varchar(1024)  NULL,
  [ChargeAmount] decimal(19, 4) NULL,

However, I have two extra fields (EvalCourseAsWhole and EvalOverallCodeCamp) I need to fill in from another table (SessionEvals).

CREATE TABLE [dbo].[SessionEvals] (
  [Id] int IDENTITY(1, 1) NOT NULL,
  [SessionId] int NOT NULL,
  [AttendeeId] int NOT NULL,
  [CourseAsWhole] int NULL,
  [OverallCodeCamp] int NULL,

I could use an outer join for this but in this case I chose to do two selects, one of the first table in it’s entirety

// create the dictionary that will hold the tuples
var sessionEvals = SessionEvalsManager.I.GetAll();
dict = new Dictionary<Tuple<int, int>, SessionEvalsResult>();
foreach (var s in sessionEvals)
    var tuple = new Tuple<int,int>(s.sessionId,s.attendeeId);
    dict.Add(tuple, s);
foreach (var r in sessionAttendeeRecs)
        var tuple = new Tuple<int, int>(r.sessionId, r.attendeeId);
        if (dict.ContainsKey(tuple))
            var sessionEval = dict[tuple];
            r.EvalCourseAsWhole = sessionEval.CourseAsWhole ?? -1;
            r.EvalOverallCodeCamp = sessionEval.OverallCodeCamp ?? -1;
            r.EvalDone = true;

About Peter Kellner

Peter is a software professional specializing in mobile and web technologies. He has also been a Microsoft MVP since 2007. In addition, he’s a multi-course video author at Pluralsight. To read more about Peter Kellner and his experience click here. For information about how Peter Kellner might be able to help you with your project click here.

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  1. Peter Kellner says:

    Left join seems hard in linq2sql

  2. Stuart Allen says:

    Couldn’t you get the same functionality by doing a Left join?


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