Is there any way to return default values in Kotlin Data Class when using Moshi when the API return null values through JSON

Question

When JSON data comes null, then I want, it should take the default value and I do not have to null check in the Moshi Converter always.

I am using the Moshi-kotlin as well, but still, the result are the same.

{ 
        "image": null,
        "visible": null
        "name": null,
        "description": null
        "id": null,
        "subcategories": null
        "ordinal": null,
        "isEvent": null,
        "style": null
}

Here is my Data class where I am keeping its default value .

Answer 1

Make the data class entries non-nullable (remove the ?)

Then put in every place that you invoke the constructor, ?: "" . Anything that is null will be changed to an empty string

Alternatively, you could create a .invoke(...) method on the companion object and use this to process the values.

Answer 2

Consider defining two model classes:

• one that represents exactly what your server provided (things are null), and
• one that represents how your application works (things are non-null)

You can follow the EventJson example from the Moshi readme to pretty easily convert between these when you decode the server object.

class EventJsonAdapter {
  @FromJson Event eventFromJson(EventJson eventJson) {
    Event event = new Event();
    event.title = eventJson.title;
    event.beginDateAndTime = eventJson.begin_date + " " + eventJson.begin_time;
    return event;
  }

  @ToJson EventJson eventToJson(Event event) {
    EventJson json = new EventJson();
    json.title = event.title;
    json.begin_date = event.beginDateAndTime.substring(0, 8);
    json.begin_time = event.beginDateAndTime.substring(9, 14);
    return json;
  }
}

Trying to use the same object for business logic and JSON is awkward. Having different objects for each is a simple way to avoid that. Plus you can be deliberate about what happens when sending these default values back to the server.