Question

EDIT 1: Forgot to add the nested property curve ball.

UPDATE: I have chosen @mtazva’s answer as that was the preferred solution for my specific case. In retrospect, I asked a general question with a very specific example and I believe that ended up confusing everyone (or maybe just me) as to what the question was exactly. I do believe the general question has been answered as well (see the Strategy pattern answers and links). Thanks everyone!

Large switch statements obviously smell and I have seen some links on how you could do this with a dictionary that maps to functions. But I’m wondering if there is a better (or smarter way) to do this? In a way, this is a question I’ve always sort of had rolling around in the back of my head but never really had a good solution to.

This question stemmed from another question I asked earlier: How to select all the values of an object's property on a list of typed objects in .Net with C#

Here is an example class I’m working with (from an external source):

public class NestedGameInfoObject
{
    public string NestedName { get; set; }
    public int NestedIntValue { get; set; }
    public decimal NestedDecimalValue { get; set; }
}

public class GameInfo
{
    public int UserId { get; set; }
    public int MatchesWon { get; set; }
    public long BulletsFired { get; set; }
    public string LastLevelVisited { get; set; }
    public NestedGameInfoObject SuperCoolNestedGameInfo { get; set; }
    // thousands more of these
}

Unfortunately, this is coming from an external source… imagine a HUGE data dump from Grand Theft Auto or something.

And I want to get just a small cross section of a list of these objects. Imagine we want to be able to compare you with a bunch of your friends’ game info objects. An individual result for one user would look like this:

public class MyResult
{
    public int UserId { get; set; }  // user id from above object
    public string ResultValue { get; set; }  // one of the value fields from above with .ToString() executed on it
}

And an example of what I want to replace with something more manageable (believe me, I DON’T want to be maintaining this monster switch statement):

const int MATCHES_WON = 1;
const int BULLETS_FIRED = 2;
const int NESTED_INT = 3;

public static List<MyResult> GetMyResult(GameInfo[] gameInfos, int input)
{
  var output = new List<MyResult>();

  switch(input)
  {
    case MATCHES_WON:
        output = gameInfos.Select(x => new MyResult()
         {
            UserId = x.UserId, 
            ResultValue = x.MatchesWon.ToString()
         }).ToList<MyResult>();
      break;

    case BULLETS_FIRED:
        output = gameInfos.Select(x => new MyResult()
         {
            UserId = x.UserId, 
            ResultValue = x.BulletsFired.ToString()
         }).ToList<MyResult>();
      break;

    case NESTED_INT:
        output = gameInfos.Select(x => new MyResult()
         {
            UserId = x.UserId, 
            ResultValue = x.SuperCoolNestedGameInfo.NestedIntValue.ToString()
         }).ToList<MyResult>();
      break;

    // ad nauseum
  }

  return output;
}

So the question is are there any reasonable ways to manage this beast? What I’d really like is a dynamic way to get this info in case that initial object changes (more game info properties are added, for instance). Is there a better way to architect this so it’s less clumsy?

Answer 1

I think your first sentence eluded to what is probably the most reasonable solution: some form of dictionary mapping values to methods.

For example, you could define a static Dictionary<int, func<GameInfo, string>>, where each value such as MATCHES_WON would be added with a corresponding lambda that extracts the appropriate value (assuming your constants, etc are defined as shown in your example):

private static Dictionary<int, Func<GameInfo, string>> valueExtractors =
    new Dictionary<int, Func<GameInfo, string>>() {
        {MATCHES_WON,   gi => gi.MatchesWon.ToString()},
        {BULLETS_FIRED, gi => gi.BulletsFired.ToString()},
        //.... etc for all value extractions
    };

You can then use this dictionary to extract the value in your sample method:

public static List<MyResult> GetMyResult(GameInfo[] gameInfos, int input)
{
  return gameInfo.Select(gi => new MyResult()
         {
            UserId = gi.UserId, 
            ResultValue = valueExtractors[input](gi)
         }).ToList<MyResult>();
}

Outside of this option, you could potentially have some sort of file/database/stored lookup with the number and the property name, then use reflection to extract the value, but that would obviously not perform as well.