HowTo skip deserialization for a field in json4s

Question

Here is my json:

{
  "stringField" : "whatever",
  "nestedObject": { "someProperty": "someValue"}
}

I want to map it to

case class MyClass(stringField: String, nestedObject:String)

nestedObject should not be deserialized, I want json4s to leave it as string.

resulting instance shouldBe:

val instance = MyClass(stringField="whatever", nestedObject= """ { "someProperty": "someValue"} """)

Don't understand how to do it in json4s.

Answer 1

You can define a custom serializer:

case object MyClassSerializer extends CustomSerializer[MyClass](f => ( {
  case jsonObj =>
    implicit val format = org.json4s.DefaultFormats
    val stringField = (jsonObj \ "stringField").extract[String]
    val nestedObject = compact(render(jsonObj \ "nestedObject"))

    MyClass(stringField, nestedObject)
}, {
  case myClass: MyClass =>
    ("stringField" -> myClass.stringField) ~
      ("nestedObject" -> myClass.nestedObject)
}
))

Then add it to the default formatter:

implicit val format = org.json4s.DefaultFormats + MyClassSerializer
println(parse(jsonString).extract[MyClass])

will output:

MyClass(whatever,{"someProperty":"someValue"})

Code run at Scastie