Convert a row-List Cassandra table to a JSON format using scala - json

Question

I want to convert a Cassandra table into JSON format using scala; this is the code I use to connect to Cassandra and show the table:
val cluster = Cluster.builder().addContactPoint("localhost").build()
val session = cluster.connect("MyKeySpace")
try {
val a = session.execute("Select* from users")
println(a.all()) //Show as a Row-List
//Sample --> [Row[10, Fri Jan 19 04:05:01 MST 2018, 9217], Row[10, Mon Feb 19 04:05:01 MST 2018, 9217], Row[10, Mon Mar 19 04:05:01 MDT 2018, 9217]]
/** I have this example for the convertion but do not supports that format **/
case class Sample (Registro: Int,Fecha: String,Valor: String )
val agregado = Sample(999,"Wed May 20 15:19:21 MDT 31063531","982556517")
val json= ("Reg_Num:"->agregado.Registro)~("TimeStamp:"->agregado.Fecha) ~ ("Value:"->agregado.Valor) //This is a List
val JsonExam = println(compact(render(json)))
println ( pretty(render(json)) )
}
catch
{
case e: Exception => println(s"msg=${e.getMessage}")
}
Basically, I want to convert from this format:
[Row[10, Fri Jan 19 04:05:01 MST 2018, 9217], Row[12, Mon Feb 20 04:05:01 MST 2018, 9216], Row[18, Tue Mar 21 04:05:01 MDT 2018, 9215]]
To this:
{
"Reg_Num:" : 10,
"TimeStamp:" : "Fri Jan 19 04:05:01 MST 2018",
"Value:" : "9217"
},
{
"Reg_Num:" : 12,
"TimeStamp:" : "Mon Feb 20 04:05:01 MST 2018",
"Value:" : "9216"
},
{
"Reg_Num:" : 18,
"TimeStamp:" : "Tue Mar 21 04:05:01 MDT 2018",
"Value:" : "9215"
}

Answer 1

It will depend on which Json library you are using. In Play Json, we create "Writes" methods which take an instance of a case class and convert it to Json. When these are implicit then the compiler will do it "automatically" when needed. For example:
....
import play.api.libs.json._
case class Sample(Registro: Int, Fecha: String, Valor: String ){
object Sample {
implicit val SamplenWrites = new Writes[Sample] {
def writes(sample: Sample):JsValue = Json.obj(
"reg_rum"-> sample.Registro,
"timeStamp"-> sample.Fecha,
"value" -> sample.Valor)
}
}
}
Json.obj("samples" -> Sample(5, "Fri Jan 19", "9200"))