PlayFramework obj to json - json

Question

From: https://www.playframework.com/documentation/2.3.x/ScalaJsonHttp
Playframework Scala way:
case class Location(lat: Double, long: Double)
case class Place(name: String, location: Location)
object Place {
var list: List[Place] = {
List(
Place(
"Sandleford",
Location(51.377797, -1.318965)
),
Place(
"Watership Down",
Location(51.235685, -1.309197)
)
)
}
}
implicit val locationWrites: Writes[Location] = (
(JsPath \ "lat").write[Double] and
(JsPath \ "long").write[Double]
)(unlift(Location.unapply))
implicit val placeWrites: Writes[Place] = (
(JsPath \ "name").write[String] and
(JsPath \ "location").write[Location]
)(unlift(Place.unapply))
Next we write our Action:
def listPlaces = Action {
val json = Json.toJson(Place.list)
Ok(json)
}
Is there is simpler way to do it? Without all this obvious implicits ? I just want it convert all object structure as it is. Like on JS when work with JSON.
Assuming i'm O.K. with default field names and default object structure. Can I I make use of "default advantage-sugar" ?.
UPDATE:
As simple as in NodeJS for example:
var list = {"places":[
{"name":"Sandleford", "location":{"lat": "1", "long": "222"}},
{"name":"Watership Down", "location":{"lat": "2", "long": "333"}},
]}
router.get('/', function(req, res) {
res.json(list);
});
There is no question what should be localized and how.
Or like in java (pure jackson):
List list = Arrays.asList(place1, place2);
ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
String json = ow.writeValueAsString(list);
Where class Place defined with no annotation (but with getters and setters, what I don't like though).
I may use jackson in scala, but I wonder about 'official defaults'.. in playframewok for scala to go with less code (like it is supposed to be).

Answer 1

Json.writes[T]
If all you want is literal serialization to Json, and you don't want to write the Writes instances yourself you can use the Json.writes[T] macro to generate the Writes[T] for you.
import play.api.libs.json._
case class Location(lat: Double, long: Double)
case class Place(name: String, location: Location)
object Place {
val list: List[Place] = {
List(
Place(
"Sandleford",
Location(51.377797, -1.318965)
),
Place(
"Watership Down",
Location(51.235685, -1.309197)
)
)
}
}
object JsonStuff {
implicit val locationWrites: Writes[Location] = Json.writes[Location]
implicit val placeWrites: Writes[Place] = Json.writes[Place]
}
Then on the repl,
scala> import JsonStuff._
import JsonStuff._
scala> import play.api.libs.json._
import play.api.libs.json._
scala> Json.toJson(Place.list)
res0: play.api.libs.json.JsValue = [{"name":"Sandleford","location":{"lat":51.377797,"long":-1.318965}},{"name":"Watership Down","location":{"lat":51.235685,"long":-1.309197}}]
Json Literals
If you really want to you can of course just create and manipulate the JsValue directly. For instance
object Place {
val JsList =
JsArray(
Seq(
Json.obj(
("name" -> "Sandleford"),
("location" ->
Json.obj(
("lat" -> 51.377797),
("long" -> -1.318965)))),
Json.obj(
("name" -> "Watership Down"),
("location" ->
Json.obj(
("lat" -> 51.235685),
("long" -> -1.309197))))))
}
On the repl,
scala> Place.JsList
res0: play.api.libs.json.JsArray = [{"name":"Sandleford","location":{"lat":51.377797,"long":-1.318965}},{"name":"Watership Down","location":{"lat":51.235685,"long":-1.309197}}]
Though this approach can be quite difficult to work with for all but the most trivial applications and I would highly recommend against it.

Answer 2

As isomarcte already answered. I had to do this (and this almost satisfied me as noise-free solution):
case class Location(lat: Double, long: Double)
case class Place(name: String, location: Location)
// little noise (just too lines, but that could be even one #Json. Could..
object JsonStuff {
implicit val locationWrites: Writes[Location] = Json.writes[Location]
implicit val placeWrites: Writes[Place] = Json.writes[Place]
}
object Application extends Controller {
def places = Action {
import play.api.libs.json._
val list: List[Place] = {
List(
Place(
"Sandleford",
Location(51.377797, -1.318965)
),
Place(
"Watership Down",
Location(51.235685, -1.309197)
)
)
}
import JsonStuff._
Ok(Json.toJson(list))
}
And I had to:
to move case classes out - to make them stand alone
delete Place object to make list stands by itself
otherwise I had: No unapply function found error.
(known limitations)
and sequence of putting implicit val ..writers does matter - Place should know about Location .. since those writers are macros.. Like in JS :) heh.
otherwise you will get NullPotinter exception
(a little bit overcomplicated as for me)