Why System.Version in JSON string does not deserialize correctly?

Question

Context: I need to pass an object containing a large number of properties/fields (to UI Layer from Middle Tier Layer). Among this list of properties, one is of type Version which is not getting deserialized correctly from JSON string format. I have a chosen JSON format over XML as JSON serialization to string will return short string result.

Problem: System.Version does not get deserialized correctly. I have tried two different .NET Libraries. Following are the code snippets for each:

Code Snippet 1 using ServiceStack .NET library:

        var version = new Version(1, 2, 3, 0);
        string reportJSON = JsonSerializer.SerializeToString<Version>(version);
        //{"Major":1,"Minor":2,"Build":3,"Revision":0,"MajorRevision":0,"MinorRevision":0}


        Version report2 = JsonSerializer.DeserializeFromString<Version>(reportJSON);
        string reportJSON2 = JsonSerializer.SerializeToString<Version>(report2);
        //{"Major":0,"Minor":0,"Build":-1,"Revision":-1,"MajorRevision":-1,"MinorRevision":-1}

Code Snippet 2 using Newtonsoft .NET library but with same result:

        var version = new Version(1, 2, 3, 0);
        string reportJSON = JsonConvert.SerializeObject(version);
        //{"Major":1,"Minor":2,"Build":3,"Revision":0,"MajorRevision":0,"MinorRevision":0}


        Version report2 = JsonConvert.DeserializeObject<Version>(reportJSON);
        string reportJSON2 = JsonConvert.SerializeObject(report2);
        //{"Major":0,"Minor":0,"Build":-1,"Revision":-1,"MajorRevision":-1,"MinorRevision":-1}

How to fix this? Or Which other JSON.NET library can work correctly?

Answer 1

The Newtonsoft.Json library provides a set of common converters in the Newtonsoft.Json.Convertersnamespace, including a VersionConverter you can use to serialize and deserialize System.Version.

Note that you have to use the VersionConverterboth for serialization and deserialization, though.
That's because standard serialization would generate eg.:{"Major":1,"Minor":2,"Build":3,"Revision":0,"MajorRevision":0,"MinorRevision":0} while VersionConverterdeserialization expects a simple string as in "1.2.3".

So usage would be:

using Newtonsoft.Json;
using Newtonsoft.Json.Converters;  

string s = JsonConvert.SerializeObject(version, new VersionConverter());
Version v = JsonConvert.DeserializeObject<Version>(s, new VersionConverter());

I'm not sure what's the first version of Newtonsoft.Jsonthat includes that converter. Mine has it and it's 5.0.6.

Answer 2

The properties of the Version class have no setter. They just return the value of their corresponding private fields. Therefore, the deserializer is not able to change their values.

But with Json.NET you can write a custom converter class which handles the deserialization of the Version class.

Beware: This code has not been tested very well...

public class VersionConverter : JsonConverter
{
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        // default serialization
        serializer.Serialize(writer, value);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        // create a new Version instance and pass the properties to the constructor
        // (you may also use dynamics if you like)
        var dict = serializer.Deserialize<Dictionary<string, int>>(reader);
        return new Version(dict["Major"], dict["Minor"], dict["Build"], dict["Revision"]);
    }

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

Then you have to specify that you want to use the converter:

var v = new Version(1, 2, 3, 4);
string json = JsonConvert.SerializeObject(v);

var v2 = JsonConvert.DeserializeObject<Version>(json, new VersionConverter());

Json.NET decides itself whether to use one of the converters you specified. So you can always specify the converter, as shown below. Json.NET will use one of your converters if they match a type within SomeClass.

var result = JsonConvert.DeserializeObject<SomeClass>(json, new VersionConverter());