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

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"
}

easier could be simply use "select json ...": docs.datastax.com/en/cql/3.3/cql/cql_using/useQueryJSON.html — Alex Ott
– Alex Ott, Commented Jan 26, 2018 at 19:56
And how do i do for print a format like this pretty(render(json)) — Jorge Ivansevick
– Jorge Ivansevick, Commented Jan 29, 2018 at 18:03

wwkudu · Accepted Answer · 2018-01-26 04:14:33Z

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"))

edited Jan 26, 2018 at 4:14

wwkudu

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answered Jan 25, 2018 at 23:12

Zolani Maghwebu

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1 Comment

Xantium Over a year ago

Although code is almost always essential for any post including an explanation is also essential. Remember it's not only about correcting things but also telling people where they went wrong and how they can go about not doing the mistake again.

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