JSON

{
  "data": [
    {
      "id": "x1_1",
      "type": "x1"
    },
    {
      "id": "x2_1",
      "type": "x2",
      "children": [
        {
          "id": "y1_1",
          "type": "y1"
        },
        {
          "id": "y2_1",
          "type": "y2",
          "connectedItems": [
            "x1_1"
          ]
        }      
    }
  ]
}

Data classes

interface X {
  val id: String
}

interface Y {
  val id: String
}

data class D1(data: Array<X>)

data class X1(id): X
data class X2(id, children: Array<Y>): X

data class Y1(id): Y
data class Y2(id, connectedItems): Y

If there any possibility to realize deserialization for this case (according

type

field)?

Not really for now, such format is not supported yet

Is there any plans to support such format?

Yes, there are such plans, but no ETA for it yet. I think it is possible, using intermediate representation via JSON tree: https://github.com/Kotlin/kotlinx.serialization/blob/master/runtime/jvm/src/test/kotlin/kotlinx/serialization/formats/json/JsonTreeAndMapperTest.kt#L35

Do you have a plan to solve this problem in next release?

yes

Is there any aproximate date?

I think it would be around 1.3.20 Possibly eap library releases will follow Kotlin eap's

Coming soon?

Yes

Will

by type

deserialization (like in Jackson) be available later?

Yes, we have it in the roadmap

Is there any example of custom

by type

deserialization?

I haven't looked precisely at your code, but maybe this sample https://github.com/kotlin/kotlinx.serialization/blob/master/runtime/common/src/test/kotlin/kotlinx/serialization/json/JsonTreeAndMapperTest.kt could help

Nonstrict mode required 🙂