Deserializing heterogenous JSON array into covariant List<> using Json.NET

Question

I have a JSON-array containing objects of different types with different properties. One of the properties is called \"type\" and determines the type of the array item. Here

Answer 1

The CustomCreationConverter should be able to handle this.

Answer 2

Here is an example using CustomCreationConverter.

public class JsonItemConverter :  Newtonsoft.Json.Converters.CustomCreationConverter<Item>
{
    public override Item Create(Type objectType)
    {
        throw new NotImplementedException();
    }

    public Item Create(Type objectType, JObject jObject)
    {
        var type = (string)jObject.Property("valueType");
        switch (type)
        {
            case "int":
                return new IntItem();
            case "string":
                return new StringItem();
        }

        throw new ApplicationException(String.Format("The given vehicle type {0} is not supported!", type));
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        // Load JObject from stream
        JObject jObject = JObject.Load(reader);

        // Create target object based on JObject
        var target = Create(objectType, jObject);

        // Populate the object properties
        serializer.Populate(jObject.CreateReader(), target);

        return target;
    }
}

public abstract class Item
{
    public string ValueType { get; set; }

    [JsonProperty("valueTypeId")]
    public int ValueTypeId { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    public new virtual string ToString() { return "Base object, we dont' want base created ValueType=" + this.ValueType + "; " + "name: " + Name; }
}

public class StringItem : Item
{
    [JsonProperty("value")]
    public string Value { get; set; }

    [JsonProperty("numberChars")]
    public int NumberCharacters { get; set; }

    public override string ToString() { return "StringItem object ValueType=" + this.ValueType + ", Value=" + this.Value + "; " + "Num Chars= " + NumberCharacters; }

}

public class IntItem : Item
{
    [JsonProperty("value")]
    public int Value { get; set; }

    public override string ToString() { return "IntItem object ValueType=" + this.ValueType + ", Value=" + this.Value; }
}

class Program
{
    static void Main(string[] args)
    {
        // json string
        var json = "[{\"value\":5,\"valueType\":\"int\",\"valueTypeId\":1,\"name\":\"numberOfDups\"},{\"value\":\"some thing\",\"valueType\":\"string\",\"valueTypeId\":1,\"name\":\"a\",\"numberChars\":11},{\"value\":2,\"valueType\":\"int\",\"valueTypeId\":2,\"name\":\"b\"}]";

        // The above is deserialized into a list of Items, instead of a hetrogenous list of
        // IntItem and StringItem
        var result = JsonConvert.DeserializeObject<List<Item>>(json, new JsonItemConverter());

        foreach (var r in result)
        {
            // r is an instance of Item not StringItem or IntItem
            Console.WriteLine("got " + r.ToString());
        }
    }
}

Answer 3

It could also be implemented it with my JsonSubTypes library in a declarative way:

[JsonConverter(typeof(JsonSubtypes), "valueType")]
[JsonSubtypes.KnownSubType(typeof(IntItem), "int")]
[JsonSubtypes.KnownSubType(typeof(StringItem), "string")]
public abstract class Item
{
    public string ValueType { get; set; }

    [JsonProperty("valueTypeId")]
    public int ValueTypeId { get; set; }

    [JsonProperty("name")]
    public string Name { get; set; }

    public override string ToString()
    {
        return "Base object, we dont' want base created ValueType=" + this.ValueType + "; " + "name: " + Name;
    }
}

public class StringItem : Item
{
    [JsonProperty("value")]
    public string Value { get; set; }

    [JsonProperty("numberChars")]
    public int NumberCharacters { get; set; }

    public override string ToString()
    {
        return "StringItem object ValueType=" + this.ValueType + ", Value=" + this.Value + "; " +
               "Num Chars= " + NumberCharacters;
    }
}

public class IntItem : Item
{
    [JsonProperty("value")]
    public int Value { get; set; }

    public override string ToString()
    {
        return "IntItem object ValueType=" + this.ValueType + ", Value=" + this.Value;
    }
}

[TestMethod]
public void Demo()
{
    // json string
    var json =
        "[{\"value\":5,\"valueType\":\"int\",\"valueTypeId\":1,\"name\":\"numberOfDups\"}," +
        "{\"value\":\"some thing\",\"valueType\":\"string\",\"valueTypeId\":1,\"name\":\"a\",\"numberChars\":11}," +
        "{\"value\":2,\"valueType\":\"int\",\"valueTypeId\":2,\"name\":\"b\"}]";

    var result = JsonConvert.DeserializeObject<List<Item>>(json);

    Assert.AreEqual("IntItem object ValueType=int, Value=5", result[0].ToString());
    Assert.AreEqual("StringItem object ValueType=string, Value=some thing; Num Chars= 11", result[1].ToString());
    Assert.AreEqual("IntItem object ValueType=int, Value=2", result[2].ToString());
}