How to disable TypeNameHandling when specified in attributes by using JsonSerializerSettings in Json.NET?

Question

Sometimes I need to suppress output of "$type" properties by Json.NET even when specified by JsonPropertyAttribute.ItemTypeNameHandling. How can this be done?

My root class looks like below:

public class DomainResource
{
    [JsonProperty(ItemTypeNameHandling = TypeNameHandling.Auto)]
    public List<Extension> Extensions { get; set; }
}

And in addition I have a class hierarchy for Extension such as the following:

public class Extension
{
    readonly string url;

    public string Url { get { return url; } }

    public Extension(string url)
    {
        this.url = url;
    }
}

public class IntegerExtension : Extension
{
    public IntegerExtension(string url) : base(url) { }

    [JsonProperty("ValueInteger")]
    public int Value { get; set; }
}

I want to ignore ItemTypeNameHandling in certain scenarios during serialization, but I am not able to find a way to do that. I tried setting JsonSerializerSettings with TypeNameHandling.None as input for jsonconvert when I do not want "$type" properties using the code below:

public static string SerializeObject(object value)
{
    JsonSerializerSettings jsonSettings = new JsonSerializerSettings
    {
        ContractResolver = new CamelCasePropertyNamesContractResolver(),
        NullValueHandling = NullValueHandling.Ignore,
        TypeNameHandling = TypeNameHandling.None,

    };
    jsonSettings.Converters.Add(new StringEnumConverter
    {
        CamelCaseText = true
    });
    return JsonConvert.SerializeObject(value, Formatting.None, jsonSettings);
}

And then use it as follows:

var res = new DomainResource();
res.Extensions = new List<Extension>();
res.Extensions.Add(new IntegerExtension("ewwer"){Value = 3});

var x = CustomJsonConvert.SerializeObject(res);

My desired JSON is:

{"extensions":[{"valueInteger":3,"url":"ewwer"}]}

But instead it contains "$type" properties as shown below:

{"extensions":[{"$type":"DicomtoJsonConverter.IntegerExtension, DicomtoJsonConverter","valueInteger":3,"url":"ewwer"}]}

How can I suppress output of "$type" properties without changing DomainResource class?

It's not clear what exactly you are asking? Can you share some more details about what do you expect from the code and what actually is happening? — Chetan, Oct 25 '17 at 07:27

dbc · Accepted Answer · 2017-10-25T18:03:50.630

You can use a custom ContractResolver to suppress output of type information even when specified by JsonPropertyAttribute.TypeNameHandling, JsonPropertyAttribute.ItemTypeNameHandling or JsonContainerAttribute.ItemTypeNameHandling. First, define the following contract resolver:

public class NoTypeNameHandlingContractResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);
        // Suppress JsonPropertyAttribute.TypeNameHandling
        property.TypeNameHandling = null;
        // Suppress JsonPropertyAttribute.ItemTypeNameHandling
        property.ItemTypeNameHandling = null;
        return property;
    }

    protected override JsonContract CreateContract(Type objectType)
    {
        var contract = base.CreateContract(objectType);
        if (contract is JsonContainerContract)
        {
            // Suppress JsonContainerAttribute.ItemTypeNameHandling
            ((JsonContainerContract)contract).ItemTypeNameHandling = null;
        }
        return contract;
    }
}

Then, modify CustomJsonConvert.SerializeObject() as follows:

public static class CustomJsonConvert
{
    // You may want to cache the contract resolver for best performance, see
    // https://stackoverflow.com/questions/33557737/does-json-net-cache-types-serialization-information
    static readonly JsonSerializerSettings jsonSettings;
    static CustomJsonConvert()
    {
        jsonSettings = new JsonSerializerSettings
        {
            ContractResolver = new NoTypeNameHandlingContractResolver
            {
                NamingStrategy = new CamelCaseNamingStrategy
                {
                    // These are the settings used by CamelCasePropertyNamesContractResolver by default.
                    // Change them if this is not what you want.
                    OverrideSpecifiedNames = true,
                    ProcessDictionaryKeys = true,
                },
            },
            NullValueHandling = NullValueHandling.Ignore,
            TypeNameHandling = TypeNameHandling.None,
            Converters = { new StringEnumConverter { CamelCaseText = true } },
        };
    }

    public static string SerializeObject(object value)
    {
        return JsonConvert.SerializeObject(value, Formatting.None, jsonSettings);
    }
}

If you are using a version of Json.NET that predates 9.0.1 you will need to subclass CamelCasePropertyNamesContractResolver rather than subclassing DefaultContractResolver since NamingStrategy was introduced in that release.

How to disable TypeNameHandling when specified in attributes by using JsonSerializerSettings in Json.NET?

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