Best way to define model using AndroidAnnotations @Rest and Kotlin?

Question

I am totally new to Android and Kotlin and I was looking into Android Annotations. I managed to decode a JSON response using the following code:

class ExampleModel {
    @JvmField
    final var id: Int = 0

    lateinit var title: String

    var description: String? = null

    var author: Author? = null

}

@Rest(
    rootUrl = "...",
    converters = [MappingJackson2HttpMessageConverter::class]
)

interface ExampleClient {

    @Get("/promotions")
    fun getModels(): List<ExampleModel>

}

Now it does work but there are a couple of questions I'd like to ask.

1. Is it possible to use data classes? I tried but I kept getting an error from MappingJackson2HttpMessageConverter saying that there was no constructor available.
2. Is it somehow possible to just ignore extra keys that might appear in the JSON? Let's say that I am not interested in the author data for now, is there a way to just remove its declaration without having the decoding fail with "unexpected key"?

Consider that I usually work with Swift so if you could point me to the "Codable" equivalent in Kotlin I would really appreciate it.

Cheers

Answer 1

Kotlin Data classes don't have default constructor which is usually required by json deserialization libraries. Any data class require at least one constructor argument, but you can work around it. Define default values, you can use null. For example:

data class Pojo(val name: String? = null, val age: Int? = null)

Such code will allow to use Pojo() constructor. It should work, but it's better to use json deserializer that is more kotlin native or generate data classes with AutoValue.

Jackson that you're using here allows to ignore fields with @JsonIgnoreProperties.

If you're learning Android, don't start from Android Annotations if you don't have to. It's not very popular or modern solution. I used it in few projects back in the day, those were very difficult to maintain or to introduce new developers. Look into android architecture components and jetpack - google made few nice code labs. Also for json pick Moshi or Gson.