Simple and concise way to preserve unknown properties when deserializing JSON

[Flavien]

What is your use-case and why do you need this feature?

We need a simple and concise way to no lose unknown properties when deserializing JSON. The use case is a process reading a JSON file, with some extra attributes it doesn't know about, makes some changes to the document (leaving alone the attributes it doesn't know about), and re-serialize the JSON file with the modifications.

If unknown properties are just ignored and discarded during deserialization, any extra fields that are not known by the program during deserialization will be silently lost when re-serializing.

Describe the solution you'd like

We need the ability to collect unknown properties into a Map while deserialising, and write them back when serialising. Lots of JSON libraries support this (e.g. in .NET).

[pdvrieze]

• I assume you mean here that you wish to do this in a way that you add a val otherProperties: Map<String,JsonObject> property with a marker annotation to a Serializable class, and then this property is automatically populated by all "extra" properties.
• I also assume that you don't wish to write a custom serializer for this behaviour.

I would say that such a feature is worthwhile (in Json) and I've had it in the XML format for a long time (where namespaces make this much more robust). It is not particularly hard to implement.

[Flavien]

Yes that's exactly it.

[pschichtel]

isn't this similar to #1978 ?

[sandwwraith]

Yes, I think it can be closed as duplicate of #1978