Question

I’m struggling trying to get my model type to work with Windows Azure Mobile Services. It works fine, except when I add the following member:

    [DataMemberJsonConverter(ConverterType = typeof(DictionaryJsonConverter))]
    public IDictionary<Tuple<int, int>, BoardSpaceState> pieceLocations { get; set; }


    /**
     * All of this serialization could probably be done better,
     * but I've spent enough time trying to make it work already.
     */
    public class DictionaryJsonConverter : IDataMemberJsonConverter 
    {
        public static Tuple<int, int> tupleOfString(string str)
        {
            var match = Regex.Match(str, @"\((\d+), (\d+)\)");
            // need to grab indexes 1 and 2 because 0 is the entire match
            return Tuple.Create(int.Parse(match.Groups[1].Value), int.Parse(match.Groups[2].Value));
        }

        public object ConvertFromJson(IJsonValue val)
        {
            var dict = JsonConvert.DeserializeObject<Dictionary<string, string>>(val.GetString());
            var deserialized = new Dictionary<Tuple<int, int>, BoardSpaceState>();
            foreach (var pieceLoc in dict)
            {
                deserialized[tupleOfString(pieceLoc.Key)] = (BoardSpaceState) Enum.Parse(typeof(BoardSpaceState), pieceLoc.Value);
            }
            return deserialized;
        }

        public IJsonValue ConvertToJson(object instance)
        {
            var dict = (IDictionary<Tuple<int, int>, BoardSpaceState>)instance;
            IDictionary<Tuple<int, int>, string> toSerialize = new Dictionary<Tuple<int, int>, string>();
            foreach (var pieceLoc in dict)
            {
                /** There may be an easier way to convert the enums to strings
                 * http://stackoverflow.com/questions/2441290/json-serialization-of-c-sharp-enum-as-string
                 * By default, Json.NET just converts the enum to its numeric value, which is not helpful.
                 * There could also be a way to do these dictionary conversions in a more functional way.
                 */
                toSerialize[pieceLoc.Key] = pieceLoc.Value.ToString();
            }

            var serialized = JsonConvert.SerializeObject(toSerialize);
            return JsonValue.CreateStringValue(serialized);
        }
    }

BoardSpaceState.cs:

public enum BoardSpaceState
    {
        FriendlyPieceShort,
        FriendlyPieceTall,
        OpponentPieceShort,
        OpponentPieceTall,
        None
    }

This persists to Azure just fine, and I can see the data in the management portal. However, when I try to load the data with toListAsync(), I get the following exception:

{"Object must implement IConvertible."} System.Exception {System.InvalidCastException}

at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)\r\n
at Microsoft.WindowsAzure.MobileServices.TypeExtensions.ChangeType(Object value, Type desiredType)\r\n   
at Microsoft.WindowsAzure.MobileServices.MobileServiceTableSerializer.Deserialize(IJsonValue value, Object instance, Boolean ignoreCustomSerialization)\r\n   
at Microsoft.WindowsAzure.MobileServices.MobileServiceTableSerializer.Deserialize(IJsonValue value, Object instance)\r\n   
at Microsoft.WindowsAzure.MobileServices.MobileServiceTableSerializer.Deserialize[T](IJsonValue value)\r\n   
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()\r\n   
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)\r\n   
at Microsoft.WindowsAzure.MobileServices.TotalCountList`1..ctor(IEnumerable`1 sequence)\r\n   
at Microsoft.WindowsAzure.MobileServices.MobileServiceTable`1.<ToListAsync>d__3f.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n   
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)\r\n   
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()\r\n   
at chivalry.DataManager.<withServerData>d__2.MoveNext() in c:\\Users\\Rosarch\\Documents\\Visual Studio 2012\\Projects\\chivalry\\chivalry\\DataManager.cs:line 35" string

The HRESULT is -2147467262.

What am I doing wrong?

Update:

The line I get the error is:

private IMobileServiceTable<Game> gameTable = App.MobileService.GetTable<Game>();
// ...
var games = await gameTable.ToListAsync();  // error here

For what it’s worth, I also get the same error if I just return new Dictionary<Tuple<int, int>, BoardSpaceState>() from DictionaryJsonConverter.ConvertFromJson.

Answer 1

That seems to be a bug in the Azure Mobile Services client SDK – I’ll file it with the product team, thank you for reporting it.

Meanwhile, there is a workaround which will get it working: instead of declaring the pieceLocations variable with the interface type, if you declare it with the dictionary type then it will work – here’s the code which I just tried.

public sealed partial class MainPage : Page
{
    public static MobileServiceClient MobileService = new MobileServiceClient(
        "https://YOUR-APP-NAME-HERE.azure-mobile.net/",
        "YOUR-APP-KEY-HERE"
    );

    public MainPage()
    {
        this.InitializeComponent();
    }

    /// <summary>
    /// Invoked when this page is about to be displayed in a Frame.
    /// </summary>
    /// <param name="e">Event data that describes how this page was reached.  The Parameter
    /// property is typically used to configure the page.</param>
    protected override void OnNavigatedTo(NavigationEventArgs e)
    {
    }

    private async void btnStart_Click_1(object sender, RoutedEventArgs e)
    {
        try
        {
            Game game = new Game();
            game.pieceLocations = new Dictionary<Tuple<int, int>, BoardSpaceState>();
            for (int i = 0; i < 5; i++)
            {
                for (int j = 0; j < 5; j++)
                {
                    game.pieceLocations[Tuple.Create(i, j)] = BoardSpaceState.None;
                }
            }

            game.pieceLocations[Tuple.Create(1, 2)] = BoardSpaceState.FriendlyPieceShort;
            game.pieceLocations[Tuple.Create(2, 1)] = BoardSpaceState.FriendlyPieceTall;
            game.pieceLocations[Tuple.Create(3, 4)] = BoardSpaceState.OpponentPieceShort;
            game.pieceLocations[Tuple.Create(4, 3)] = BoardSpaceState.OpponentPieceTall;

            var table = MobileService.GetTable<Game>();
            await table.InsertAsync(game);
            AddToDebug("Inserted game: ", game.Id);

            AddToDebug("Now trying to retrieve it...");

            var allGames = await table.ToListAsync();
            AddToDebug("All games, length = {0}", allGames.Count);
        }
        catch (Exception ex)
        {
            AddToDebug("Error: {0}", ex);
        }
    }

    void AddToDebug(string text, params object[] args)
    {
        if (args != null && args.Length > 0) text = string.Format(text, args);
        this.txtDebug.Text = this.txtDebug.Text + text + Environment.NewLine;
    }
}

[DataTable(Name = "Test")]
public class Game
{
    public int Id { get; set; }
    [DataMemberJsonConverter(ConverterType = typeof(DictionaryJsonConverter))]
    public Dictionary<Tuple<int, int>, BoardSpaceState> pieceLocations { get; set; }
}

public enum BoardSpaceState
{
    FriendlyPieceShort,
    FriendlyPieceTall,
    OpponentPieceShort,
    OpponentPieceTall,
    None
}

public class DictionaryJsonConverter : IDataMemberJsonConverter
{
    public static Tuple<int, int> tupleOfString(string str)
    {
        var match = Regex.Match(str, @"\((\d+), (\d+)\)");
        // need to grab indexes 1 and 2 because 0 is the entire match
        return Tuple.Create(int.Parse(match.Groups[1].Value), int.Parse(match.Groups[2].Value));
    }

    public object ConvertFromJson(IJsonValue val)
    {
        var dict = JsonConvert.DeserializeObject<Dictionary<string, string>>(val.GetString());
        var deserialized = new Dictionary<Tuple<int, int>, BoardSpaceState>();
        foreach (var pieceLoc in dict)
        {
            deserialized[tupleOfString(pieceLoc.Key)] = (BoardSpaceState)Enum.Parse(typeof(BoardSpaceState), pieceLoc.Value);
        }
        return deserialized;
    }

    public IJsonValue ConvertToJson(object instance)
    {
        var dict = (IDictionary<Tuple<int, int>, BoardSpaceState>)instance;
        IDictionary<Tuple<int, int>, string> toSerialize = new Dictionary<Tuple<int, int>, string>();
        foreach (var pieceLoc in dict)
        {
            /** There may be an easier way to convert the enums to strings
             * http://stackoverflow.com/questions/2441290/json-serialization-of-c-sharp-enum-as-string
             * By default, Json.NET just converts the enum to its numeric value, which is not helpful.
             * There could also be a way to do these dictionary conversions in a more functional way.
             */
            toSerialize[pieceLoc.Key] = pieceLoc.Value.ToString();
        }

        var serialized = JsonConvert.SerializeObject(toSerialize);
        return JsonValue.CreateStringValue(serialized);
    }
}