How to serialize a Dictionary as part of its parent object using Json.Net

Question

I'm using Json.Net for serialization. I have a class with a Dictionary:

public class Test
{
    public string X { get; set; }

    public Dictionary<string, string> Y { get; set; }
}

Can I somehow serialize this object to get the following JSON

{
    "X" : "value",
    "key1": "value1",
    "key2": "value2"
}

where "key1", "key2" are keys in the Dictionary?

Answer 1

If you're using Json.Net 5.0.5 or later and you're willing to change the type of your dictionary from Dictionary<string, string> to Dictionary<string, object> , then one easy way to accomplish what you want is to add the [JsonExtensionData] attribute to your dictionary property like this:

public class Test
{
    public string X { get; set; }

    [JsonExtensionData]
    public Dictionary<string, object> Y { get; set; }
}

The keys and values of the marked dictionary will then be serialized as part of the parent object. The bonus is that it works on deserialization as well: any properties in the JSON that do not match to members of the class will be placed into the dictionary.

Answer 2

Implement JsonConverter -derived class: the CustomCreationConverter class should be used as base class to create a custom object .

Draft version of the converter (error handling can be improved as you wish):

internal class TestObjectConverter : CustomCreationConverter<Test>
{
    #region Overrides of CustomCreationConverter<Test>

    public override Test Create(Type objectType)
    {
        return new Test
            {
                Y = new Dictionary<string, string>()
            };
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteStartObject();

        // Write properties.
        var propertyInfos = value.GetType().GetProperties();
        foreach (var propertyInfo in propertyInfos)
        {
            // Skip the Y property.
            if (propertyInfo.Name == "Y")
                continue;

            writer.WritePropertyName(propertyInfo.Name);
            var propertyValue = propertyInfo.GetValue(value);
            serializer.Serialize(writer, propertyValue);
        }

        // Write dictionary key-value pairs.
        var test = (Test)value;
        foreach (var kvp in test.Y)
        {
            writer.WritePropertyName(kvp.Key);
            serializer.Serialize(writer, kvp.Value);
        }
        writer.WriteEndObject();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject jsonObject = JObject.Load(reader);
        var jsonProperties = jsonObject.Properties().ToList();
        var outputObject = Create(objectType);

        // Property name => property info dictionary (for fast lookup).
        var propertyNames = objectType.GetProperties().ToDictionary(pi => pi.Name, pi => pi);
        foreach (var jsonProperty in jsonProperties)
        {
            // If such property exists - use it.
            PropertyInfo targetProperty;
            if (propertyNames.TryGetValue(jsonProperty.Name, out targetProperty))
            {
                var propertyValue = jsonProperty.Value.ToObject(targetProperty.PropertyType);
                targetProperty.SetValue(outputObject, propertyValue, null);
            }
            else
            {
                // Otherwise - use the dictionary.
                outputObject.Y.Add(jsonProperty.Name, jsonProperty.Value.ToObject<string>());
            }
        }

        return outputObject;
    }

    public override bool CanWrite
    {
        get { return true; }
    }

    #endregion
}

Client code:

var test = new Test
    {
        X = "123",
        Y = new Dictionary<string, string>
            {
                { "key1", "value1" },
                { "key2", "value2" },
                { "key3", "value3" },
            }
    };

string json = JsonConvert.SerializeObject(test, Formatting.Indented, new TestObjectConverter());
var deserializedObject = JsonConvert.DeserializeObject<Test>(json);

Please note: there is a potential collision between property names and key names of the dictionary.

Answer 3

You can create this converter and then assign it to your property. Took bits and pieces of of proposed solutions.

public class DictionaryToJsonObjectConverter : JsonConverter
    {
        public override bool CanConvert(Type objectType)
        {
            return typeof(IDictionary<string, string>).IsAssignableFrom(objectType);
        }

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

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            writer.WriteRawValue(JsonConvert.SerializeObject(value, Formatting.Indented));
        }
    }

Then use it in your poco class.

public class Poco
{
        [JsonProperty("myid")]
        public string Id{ get; set; }

        [JsonProperty("properties")]
        [JsonConverter(typeof(DictionaryToJsonObjectConverter))]
        public IDictionary<string, string> Properties { get; set; }
    }