Scala adding an element to JsValue before convertT[class]

I have a Kafka consumed record that will be parsed as JsValue with spray.json in scala, but I also have some data in the record's header, and I want to do:

1. Consume record with Alpakka Kafka library (done)

2. parse as json of type JsValue: kafkaRecord.record.value().parseJson (also done)

3. Append the record's header to that JsValue (HERE IS THE MAIN CONCERN)

   Header = kafkaRecord.record.headers()

   Appending should include key[String]: value(header)

4. convert to pre-defined case class using [JsValue].convertTo[<case class>]

Here is the consumed record for example:

{"id": 23, "features": "features_23"}

and want to append to it the Header to be as:

{"id": 23, "features": "features_23", "header_data":"Header_23"}

Then convert to case class:

case class recordOfKafka(id: Int, features: String, header_data: String)

Assuming some functions that get the string value of the record and header:

@ def getKafkaRecord(): String = """
  {"id":1,"features":"feature_23"}
  """ 
defined function getKafkaRecord

@ def getKafkaHeader(): String = """
  {"header_data":"header_23"}
  """ 
defined function getKafkaHeader

And the model with formatter:

@ import spray.json._
@ import DefaultJsonProtocol._

@ case class SomeModel(id: Int, features: String, header_data: String) 
defined class SomeModel

@ implicit val someModelFormatter = jsonFormat3(SomeModel) 
someModelFormatter: RootJsonFormat[SomeModel] = spray.json.ProductFormatsInstances$$anon$3@6c1e40d9

You can parse record value and header in separate json objects, and then combine their fields together:

@ // parse as json object, convert to map
@ JsObject(
    getKafkaRecord.parseJson.asJsObject.fields ++
      getKafkaHeader.parseJson.asJsObject.fields
  ).convertTo[SomeModel] 
res15: SomeModel = SomeModel(
  id = 1,
  features = "feature_23",
  header_data = "header_23"
)

One thing to take care about is that, if you want to use .asJsObject you must be sure that the records are json objects, like if you receive:

[{"key":"value"},{"key":"value_2"}]

It'll throw exceptions since this is an json array and cannot be converted to json object! You can also use try or pattern matching for conversion to JsObject to be safer.