Add optional property with json transformers in playframework 2.4 - json

Question

I can't understand, how can i add optional property with json transformer.
I want merge two json objects (list and calendars) without or with dynamic list of properties (for example without owner):
calendar1 = {id:1, name: "first", description:"my first calendar", owner: 1}
calendar2 = {id:2, name: "second", owner: 1}
list = [{id: 1, settings: []}, {id: 2, settings: []}]
and result must be
{calendars:
[
{id:1, name: "first", description:"my first calendar", settings: []},
{id:2, name: "second", settings: []}
]
}

Answer 1

I'll assume the following json trees
val calendar1 = Json.parse("""{"id":1, "name": "first", "description":"my first calendar", "owner": 1}""")
val calendar2 = Json.parse("""{"id":2, "name": "second", "owner": 1}""")
You need to add settings to each calendar, then remove the owner if it exists.
Putting a value in branch settings is explained in the documentation
val addSettings = __.json.update((__ \ "settings").json.put(Json.arr()))
Dropping the owner is also explained
val removeOwner = (__ \ "owner").json.prune
Now you can define the transformer to be applied to each of your calendar object
val transformer = addSettings andThen removeOwner
With that in place there are multiple options depending on how your data is actually modeled. If you have a Seq of calendars as in
val calendars = Seq(calendar1, calendar2)
you can do
val normalizedCalendars = calendars.map(_.transform(transformer))
This gives you a Seq[JsResult[JsObject]] which you want to transform into a JsResult[Seq[JsObject]].
I am pretty sure there is a way to do it using play's functional syntax (see play.api.libs.functional and play.api.libs.functional.syntax) but this part of play is not well documented and I haven't gotten around to studying Applicatives yet even though I have a feel for what they do.
Instead, I rely on the following code inspired by scala's Future#sequence
def sequence[A, M[X] <: TraversableOnce[X]](in: M[JsResult[A]])(implicit cbf: CanBuildFrom[M[JsResult[A]], A, M[A]]): JsResult[M[A]] = {
val empty: JsResult[mutable.Builder[A, M[A]]] = JsSuccess(cbf(in))
in.foldLeft(empty) {(jracc,jrel) => (jracc,jrel) match {
case (JsSuccess(builder,_), JsSuccess(a,p)) =>JsSuccess(builder+=a, p)
case (ra#JsError(builderErrors), re#JsError(errors)) =>JsError.merge(ra, re)
case (JsSuccess(_,_), re#JsError(errors)) => re
case (ra#JsError(builderErrors), JsSuccess(_,_)) => ra
}} map (_.result())
}
With that you can write :
val calendarArray = sequence(normalizedCalendars).map(v=>Json.obj("calendars"->JsArray(v)))
which will give you a JsResult[JsObject]. As long as your original calendars are indeed JsObjects you will get a JsSuccess. You can verify the output structure with :
calendarArray.foreach(println)
which returns :
{"calendars":[{"id":1,"name":"first","description":"my first calendar","settings":[]},{"id":2,"name":"second","settings":[]}]}
which is the same as what you asked modulo some whitespace
{
"calendars":[
{"id":1,"name":"first","description":"my first calendar","settings":[]},
{"id":2,"name":"second","settings":[]}
]
}

Answer 2

Start with:
scala> case class Calendar(id:Int,name:String,description:Option[String],owner:Int)
defined class Calendar
scala> case class CalendarRow(id:Int,name:String,description:Option[String],settings:Seq[String]=Seq.empty)
defined class CalendarRow
scala> def append(calendars:Calendar*) = calendars.map(c => CalendarRow(c.id,c.name,c.description))
append: (calendars: Calendar*)Seq[CalendarRow]
scala> val calendar1 = Calendar(1,"first",Option("my first calendar"),1)
calendar1: Calendar = Calendar(1,first,Some(my first calendar),1)
scala> val calendar2 = Calendar(2, "second",None,1)
calendar2: Calendar = Calendar(2,second,None,1)
scala> val list = append(calendar1,calendar2)
list: Seq[CalendarRow] = ArrayBuffer(CalendarRow(1,first,Some(my first calendar),List()), CalendarRow(2,second,None,List()))

Answer 3

Many thanks to #Jean and comments in "Unveiling Play 2.1 Json API - Part 3 : JSON Transformers"
It's hard understanding things like and, andThen, andKeep, keepAnd in JSON transformers for me (I can not find any detailed descriptions with examples), but i found some templates for my question:
Optional property in JSON:
With Reader
(__ \ "id").json.pick[JsString].flatMap{
case id if id.equals(JsString(accountId)) =>
(__ \ "primary").json.put(JsBoolean(true))
case _ =>
Reads.pure(Json.obj())
}
With Json.obj()
(__ \ "id").json.pick[JsString].map{
case id if id.equals(JsString(accountId)) =>
Json.obj("primary" -> true)
case _ =>
Json.obj()
}