How to set Json.NET ContractSerializer for a certain specific type instead of globally?

Question

I want to set a contract serializer just for certain types in my ASP.NET Web API application. I can set the settings globally in the App_Start/FormatterConfig.cs like this:

public static void RegisterGlobalFormatters(MediaTypeFormatterCollection formatters)
{
    jsonSerializerSettings.ContractResolver = new CriteriaContractResolver(new List<string>(new string[]{"mdData", "name", "label"}));

...

but how can I just apply this to one or more specific class types?

The reason I want to do this is because I need to be able to set what fields should be serialized at runtime based on configuration or parameters to the web service similar to these examples:

Using JSON.net, how do I prevent serializing properties of a derived class, when used in a base class context?

http://json.codeplex.com/discussions/347610

score 4 · Answer 1 · answered Sep 20 '12 at 08:45

4

You have a few options:

Create a custom type that is handled by a custom formatter. This custom type could specify (in some manner) what fields need to be serialized (and that information then fed into a Json serializer)
Look at per controller configuration (see here) to try and setup the formatter as requried

answered Sep 20 '12 at 08:45

Chris

772
3
8

Your first option led me to make a custom JsonConverter which is more low level than a formatter but I couldn't figure out how to specify a formatter for a particular type. – Rn222 Sep 24 '12 at 20:55

Rn222 · Accepted Answer · 2012-09-25T13:25:20.793

I ended up using a JsonConverter that only writes the parameters that are specified in the "properties" list. It's more low level than a ContractResolver or a formatter, but I don't think it's possible to configure either one for a specific type.

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

    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)
    {
        List<string> properties = new List<string>(new string[] { "Name", "Label" });

        writer.WriteStartObject();
        foreach (MemberInfo mi in value.GetType().GetMembers(BindingFlags.GetField | BindingFlags.Instance | BindingFlags.Public) )
        {
            PropertyInfo p = mi as PropertyInfo;

            if (p != null && p.GetCustomAttributes(typeof(JsonIgnoreAttribute), true).Length == 0 && properties.Contains(p.Name))
            {
                writer.WritePropertyName(p.Name);
                serializer.Serialize(writer, p.GetValue(value, new object[] { }));
            }
        }
        writer.WriteEndObject();
    }
}

This can be applied to a class using the attribute:

[JsonConverter(typeof(ResourceConverter))]

This seems like a hack though, I think I should use the contract resolver to get the list of properties to serialize instead of using reflection directly, but I'm not sure how.

score 0 · Answer 3 · answered Sep 20 '12 at 12:46

0

I would try creating something like this

public class MyJsonFormatter : JsonMediaTypeFormatter
    {
        public override bool CanWriteType(Type type)
        {
            return type == typeof(MyClass);
        }
    }

and then insert this into the beginning of the formatters collection

answered Sep 20 '12 at 12:46

Darrel Miller

139,164
32
194
243

It seems to only choose the formatter once per request based on the type of the root object that is being serialized. It won't work in my case because I have a wrapper object which I don't want to apply the settings to. – Rn222 Sep 20 '12 at 16:37

How to set Json.NET ContractSerializer for a certain specific type instead of globally?

3 Answers3

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