Serialisation of Object to Array

Question

I have an object:

[JsonConverter(typeof(MessageConverter))]
public class Message
{
    [JsonProperty(Order = 1)]
    public long Id { get; set; }
    [JsonProperty(Order = 2)]
    public string Msg { get; set; }
    [JsonProperty(Order = 3)]
    public int Timestamp { get; set; }
}

Which I would like to serialise into an array in JSON of the following form:

[long, string, int]

This class would be nested in a hierarchy, so automatic conversion would be preferred.

I am currently using the following code, but this seems to contain a significant amount of repetition.

I was wondering if there were an attribute/more compact solution that would allow JSON.NET to use the provided attributes to provide the same functionality without the converter.

public class MessageConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Message);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var arr = serializer.Deserialize<JToken>(reader) as JArray;

        if (arr == null || arr.Count != 3)
            throw new JsonSerializationException("Expected array of length 3");

        return new Message
        {
            Id = (long)arr[0],
            Msg = (string)arr[1],
            Timestamp = (int)arr[2]
        };
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var msg = value as Message;
        var obj = new object[] { msg.Id, msg.Msg, msg.Timestamp };
        serializer.Serialize(writer, obj);
    }
}

Robert Levy · Accepted Answer · 2014-09-19 01:00:14Z

1

If you are looking for that particular output, I don't think you'll find a cleaner solution than what you have. If your real goal is to serialize JSON in a compact way, look to standards like BSON or ProtoBuf

answered Sep 19, 2014 at 1:00

Robert Levy

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2 Comments

user1112560 Over a year ago

Thank you, I am looking for compactness of code rather than compactness of output. It looks possible for a general solution to exist, so I'll probably end up coding my own. I'll wait a while longer then accept your answer for the time-being.

Robert Levy Over a year ago

yeah if you dont need this exact output, using a protobuf or bson library would also reduce your code since the general solution will be in that lib

codebased · Accepted Answer · 2014-09-19 00:57:55Z

This should do your job. I just wrote for WRITE i.e. output.

namespace Test
{
    using Newtonsoft.Json;
    using Newtonsoft.Json.Linq;
    using System;
    using System.Collections;
    using System.Reflection;

    /// <summary>
    /// Defines the custom JSON Converter of collection type that serialize collection to an array of ID for Ember.
    /// </summary>
    public class CustomConverter : JsonConverter
    {
        /// <summary>
        /// Define the property name that is define in the collection type.
        /// </summary>
        private readonly string IDKEY = "Id";

        private readonly string MSGKEY = "Msg";

        private readonly string TIMEKEY = "Timestamp";

        /// <summary>
        /// It is write only convertor and it cannot be read back.
        /// </summary>
        public override bool CanRead
        {
            get { return false; }
        }

        /// <summary>
        /// Validate that this conversion can be applied on IEnumerable type only.
        /// </summary>
        /// <param name="objectType">type of object</param>
        /// <returns>Validated value in boolean</returns>
        public override bool CanConvert(Type objectType)
        {
            return objectType == typeof(Message);
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue,
            JsonSerializer serializer)
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// Write JSON data from IEnumerable to Array.
        /// </summary>
        /// <param name="writer">JSON Writer</param>
        /// <param name="value">Value of an object</param>
        /// <param name="serializer">JSON Serializer object</param>
        public override void WriteJson(JsonWriter writer, object item, JsonSerializer serializer)
        {
            JArray array = new JArray();
            PropertyInfo prop = item.GetType().GetProperty(IDKEY);
            if (prop != null && prop.CanRead)
            {
                array.Add(JToken.FromObject(prop.GetValue(item, null)));
            }

            prop = item.GetType().GetProperty(MSGKEY);
            if (prop != null && prop.CanRead)
            {
                array.Add(JToken.FromObject(prop.GetValue(item, null)));
            }

            prop = item.GetType().GetProperty(TIMEKEY);
            if (prop != null && prop.CanRead)
            {
                array.Add(JToken.FromObject(prop.GetValue(item, null)));
            }


            array.WriteTo(writer);
        }
    }
}

You are telling JSON.NET that you want to use custom convertor. so where ever you want to use it, you will have to call through attribute.

I am also doing something similar and I have to call converter manually.

  /// <summary>
        /// Gets or sets collection of documents.
        /// </summary>
        [JsonConverter(typeof(IDWriteListConverter))]
        public ICollection<Document> Documents { get; set; }

        /// <summary>
        /// Gets or sets collection of comments.
        /// </summary>
        [JsonConverter(typeof(IDWriteListConverter))]
        public ICollection<Comment> Comments { get; set; }

        /// <summary>
        /// Gets or sets the collection of transactions.
        /// </summary>
        [JsonConverter(typeof(IDWriteListConverter))]
        public virtual ICollection<Transaction> Transactions { get; set; }

This doesn't answer my question at all. A working converter has already been supplied in the OP which provides more functionality with less code.

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