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I'm trying to group common properties together on a data class and want to flatten that to other objects, e.g.

```{"id": "", "name": "", "email":""}```
 should serialize onto

```data class User(val id: String, val common: Common) { data class Common(val name: String, val email: String)}```
what am I looking for? is there an API for that use case or do I need to handroll everything?

there isn't an equivalent to `@JsonUnwrapped` like other frameworks, so you'll have to do it yourself

it's not that much work with a <https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#composite-serializer-via-surrogate|surrogate serializer> though

or alternatively, if you can structure your classes like
```interface Common {
    val name: String,
    val email: String,
}

@Serializable
data class User(
    val id: String,
    override val name: String,
    override val email: String,
) : Common```
then it'll directly produce the JSON you want

right, that requires me to duplicate 30 attributes on 10 classes though