c# Json.net immutable class

Question

I saw other similar questions/answers but none show both serialization/deserialization

Example:

public class DeepNested {
    [JsonProperty]
    int X { get; }

    [JsonProperty]
    int Y { get; }

    public DeepNested(int x, int y) { X = x; Y = y; }

    [JsonConstructor]
    public DeepNested(DeepNested dn) { X = dn.X; Y = dn.Y; }
}

public class Nested {
    [JsonProperty]
    DeepNested DN { get; }

    [JsonProperty]
    int Z { get; }

    [JsonProperty]
    int K { get; }

    [JsonConstructor]
    public Nested(DeepNested dn, int z, int k) { DN = new DeepNested(dn); Z = z; K = k; }
}

public class C {
    [JsonProperty]
    Nested N { get; }

    [JsonConstructor]
    public C(Nested n) { N = n; }
}

class Program {
    static void Main(string[] args) {
        var deepNested = new DeepNested(1,2);
        var nested = new Nested(deepNested, 3, 4);
        C c = new C(nested);
        string json = JsonConvert.SerializeObject(c);
        C c2 = JsonConvert.DeserializeObject<C>(json);
        Console.WriteLine(json);
    }
}

I get an exception on DeepNested.DeepNested(DeepNested dn)

System.NullReferenceException: 'Object reference not set to an instance of an object.'

The debugger shows dn is null

This seems be a serious limitation of Json.NET unless I'm missing something ?

I'm trying for example to serialize a C object to json and then deserialize it back — kofifus
– kofifus, Commented Jul 6, 2018 at 3:57
Have you tried creating parameterless constructor and making the properties have getter and setter both — Ipsit Gaur
– Ipsit Gaur, Commented Jul 6, 2018 at 3:59
class DeepNested -> move [JsonConstructor] to public DeepNested(int x, int y) constructor — vasily.sib
– vasily.sib, Commented Jul 6, 2018 at 5:39

vasily.sib · Accepted Answer · 2018-07-06 05:41:33Z

3

@IpsitGaur is right, commonly you should have a default public constructor and publicly accessable properties (mutable). But JSON.Net is a very powerfull tool!

If you need to handle non-default constructor, you may use JsonConstructorAttribute. For your code, example may be like this:

public class Nested
{
    public int X { get; }
    public int Y { get; }

    [JsonConstructor]
    Nested(int x, int y) { X=x; Y=y; }
}

public class C
{
    public Nested N { get; }

    [JsonConstructor]
    public C(Nested n) { N = n; }
}

var c1 = new C(new Nested(1, 2));
var json = JsonConvert.SerializeObject(c1); // produce something like "{\"n\":{\"x\":1,\"y\":2}}";
var c2 = JsonConvert.DeserializeObject<C>(json);

edited Jul 6, 2018 at 5:41

answered Jul 6, 2018 at 4:28

vasily.sib

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4 Comments

ProgrammingLlama Over a year ago

I'd recommend including an example in your answer rather than relying on an off-site resource which could be subject to link rot.

vasily.sib Over a year ago

@john Ok, I will add an example, but also I will leave this link to official JSON.Net documentation (for further reading).

kofifus Over a year ago

thanks ! I edited my question to show how a second level of nesting breaks this, pls have a look

vasily.sib Over a year ago

@kofifus, I add both (serialization/deserialization)

Mick · Accepted Answer · 2018-07-06 04:53:37Z

0

The following works...

public class Nested
{
    [JsonProperty]
    int X { get; }

    [JsonProperty]
    int Y { get; }

    public Nested(int x, int y) { X = x; Y = y; }
}

public class C
{
    [JsonProperty]
    Nested N { get; }

    public C(Nested n) { N = n; }
}

class Program
{
    static void Main(string[] args)
    {
        Nested nested = new Nested(1, 2);
        C c = new C(nested);
        string json = JsonConvert.SerializeObject(c);
        C c2 = JsonConvert.DeserializeObject<C>(json);
    }
}

answered Jul 6, 2018 at 4:53

Mick

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1 Comment

kofifus Over a year ago

thanks ! I edited my question to show how a second level of nesting breaks this, pls have a look

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