How can I make DataContractJsonSerializer serialize an object as a string?

Question

I have a struct in C# that wraps a guid. I'm using DataContractJsonSerializer to serialize an object containing an instance of that class. When I was using a guid directly, it was serialized as a plain string, but now it's serialized as a name/value pair. Here's an NUnit test and supporting code that demonstrates the problem:

    private static string ToJson<T>(T data)
    {
        DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof (T));

        using (MemoryStream ms = new MemoryStream())
        {
            serializer.WriteObject(ms, data);
            return Encoding.Default.GetString(ms.ToArray());
        }
    }

    [Serializable]
    private class ID
    {
        private Guid _value;

        public static explicit operator ID(Guid id)
        {
            return new ID { _value = id };
        }

        public static explicit operator Guid(ID id)
        {
            return id._value;
        }
    }

    [Test]
    public void IDShouldSerializeLikeGuid()
    {
        Guid guid = Guid.NewGuid();
        ID id = (ID) guid;
        Assert.That(ToJson(id), Is.EqualTo(ToJson(guid)));
    }

And the test runner output:

NUnit.Framework.AssertionException:   Expected string length 38 but was 49. Strings differ at index 0.
  Expected: ""7511fb9f-3515-4e95-9a04-06580753527d""
  But was:  "{"_value":"7511fb9f-3515-4e95-9a04-06580753527d"}"
  -----------^

How do I serialize my struct as a plain string and make my test pass?

Klarrisa

Answer 1

In this case it looks like you don't really want JSON, you want a string representation. In that case I would create an interface like this:

interface IStringSerialized
{
    String GetString();
}

Implement this interface on your ID type (and all other types that have similar requirements).

[Serializable]
class ID : IStringSerialized
{
    private Guid _value;

    public static explicit operator ID(Guid id)
    {
        return new ID { _value = id };
    }

    public static explicit operator Guid(ID id)
    {
        return id._value;
    }

    public string GetString()
    {
        return this._value.ToString();
    }
}

Then modify your serialization method to handle these special cases:

private static string ToJson<T>(T data)
{
    IStringSerialized s = data as IStringSerialized;

    if (s != null)
        return s.GetString();

    DataContractJsonSerializer serializer 
                = new DataContractJsonSerializer(typeof(T));

    using (MemoryStream ms = new MemoryStream())
    {
        serializer.WriteObject(ms, data);
        return Encoding.Default.GetString(ms.ToArray());
    }
}

Osuna

I omitted some complexity to make the problem clear, but in the real application this is in the context of a containing object that has a List<ID> in it. I want the real code to produce ["guid1", "guid2"], not [{"_value": "guid1"}, {"_value": "guid2"}]. So unfortunately, that approach won't work for me. Thanks for the idea though! – Klarrisa

Don't use Default encoding, as it will corrupt any non-ANSI characters. I'm currently dealing with Mobile phone push messages. Your code should be able to deal with other languages. Use instead, UTF8. return Encoding.UTF8.GetString(ms.ToArray()); – Diary

Answer 2

Try using the JavaScriptSerializer Class it will prevent the key, value bloat issue.

Treatment

but then you will loss all the data contracts attributes that you have in you object the you would like to serialize (like emitdefaultvalue) – Radical