Json.NET custom serialization with JsonConverter - how to get the "default" behavior

c#, json, json.net, serialization

Solution

One easy way to do it is to allocate an instance of your class then use `JsonSerializer.Populate(JsonReader, Object)`. This is the way it is done in the standard `CustomCreationConverter<T>`:

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    if (reader.Value != null && reader.ValueType == typeof(string))
    {
        return someSpecialDataTypeInstance;
    }
    else if (reader.TokenType == JsonToken.StartObject)
    {
        existingValue = existingValue ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();
        serializer.Populate(reader, existingValue);
        return existingValue;
    }
    else if (reader.TokenType == JsonToken.Null)
    {
        return null;
    }
    else
    {
        throw new JsonSerializationException();
    }
}

Limitations:

This does not handle situations when `TypeNameHandling` has been enabled and a `"$type"` property is present specifying a polymorphic subtype.

In this case you'll need to do some of the tricks use by `JsonDerivedTypeConverer<T>` in JsonConverter with Interface.

The type to be deserialized must have a parameterless constructor accessible to Json.NET. If not, and `existingValue` is null, it will be necessary to construct it manually, via `new DataType(arg1, arg2, ...)`.

Reference preservation via `PreserveReferencesHandling` is not supported.

For one approach to handle this situation see How can I choose what type to deserialize at runtime based on the structure of the json?.

Sample fiddle.

Problem

I have a JsonConverter for my class DataType. I would like to do some special handling when plain string used in Json as the value of a property of type DataType. In the case where the value is a "full" object, I would like to do the "normal" deserialization. Here is my attempt ``` public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) { if (reader.Value != null && reader.ValueType == typeof (string)) { return someSpecialDataTypeInstance; } else if (reader.TokenType == JsonToken.StartObject) { DataType dataType = serializer.Deserialize<DataType>(reader); return dataType; } else { throw new JsonSerializationException(); } } ``` But this doesn't work, because this line: DataType dataType = serializer.Deserialize(reader); causes infinite recursion. Could this be done somehow easily? (without the need to manually go property-by-property)

Original source

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