How to prevent an entire class from being serialized?

Question

I am using Newtonsoft.Json to serialize a class and all of its members. There is one particular class that many of its members are an instance of, I'd simply like to tell a class to not be serialized at all, so if any member that is an instance of that type is skipped.

Is this possible in C# by appending some sort of attribute to a class to mark it as non-serializable?

http://www.newtonsoft.com/json/help/html/SerializationAttributes.htm it will use the [NonSerializedAttribute](https://msdn.microsoft.com/en-us/library/z951x24h) — Ňɏssa Pøngjǣrdenlarp, Jun 14 '15 at 21:28
I don't think you can put it on a class, you can only put it on a member? — gnychis, Jun 14 '15 at 21:29
`Attribute 'NonSerializedAttribute' is not valid on this declaration type. It is only valid on 'field' declarations.` — gnychis, Jun 14 '15 at 21:30
Hi gnychis, if my answer helped you please accept it :) Thanks — Martin Wiboe, Aug 28 '15 at 08:56

score 4 · Answer 1 · edited May 23 '17 at 12:06

I do not think this can be done using an attribute on the class. However you should be able to do it by implementing a custom JsonConverter which always serializes and deserializes any instance of this class to null. This code implements such behavior:

class IgnoringConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteNull();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return null;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(ClassToIgnore);
    }
}

In this example, ClassToIgnore is the class you wish to ignore during serialization. Such classes should be decorated with the JsonConverter attribute:

[JsonConverter(typeof(IgnoringConverter))]
class ClassToIgnore

You can also register the converter as a default converter which is useful if you're using ASP.NET Web API.

I have included a Console application sample to demonstrate the functionality:

using System;
using Newtonsoft.Json;

/// <summary>
/// Class we want to serialize.
/// </summary>
class ClassToSerialize
{
    public string MyString { get; set; } = "Hello, serializer!";

    public int MyInt { get; set; } = 9;

    /// <summary>
    /// This will be null after serializing or deserializing.
    /// </summary>
    public ClassToIgnore IgnoredMember { get; set; } = new ClassToIgnore();
}

/// <summary>
/// Ignore instances of this class.
/// </summary>
[JsonConverter(typeof(IgnoringConverter))]
class ClassToIgnore
{
    public string NonSerializedString { get; set; } = "This should not be serialized.";
}

class IgnoringConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        writer.WriteNull();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        return null;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(ClassToIgnore);
    }
}

class Program
{
    static void Main(string[] args)
    {
        var obj = new ClassToSerialize();
        var json = JsonConvert.SerializeObject(obj);

        Console.WriteLine(json);

        obj = JsonConvert.DeserializeObject<ClassToSerialize>(json);

        // note that obj.IgnoredMember == null at this point

        Console.ReadKey();
    }
}

How to prevent an entire class from being serialized?

1 Answers1

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