Mapping a sequence of results from Slick monadic join to Json - json

Question

I'm using Play 2.4 with Slick 3.1.x, specifically the Slick-Play plugin v1.1.1. Firstly, some context... I have the following search/filter method in a DAO, which joins together 4 models:
def search(
departureCity: Option[String],
arrivalCity: Option[String],
departureDate: Option[Date]
) = {
val monadicJoin = for {
sf <- slickScheduledFlights.filter(a =>
departureDate.map(d => a.date === d).getOrElse(slick.lifted.LiteralColumn(true))
)
fl <- slickFlights if sf.flightId === fl.id
al <- slickAirlines if fl.airlineId === al.id
da <- slickAirports.filter(a =>
fl.departureAirportId === a.id &&
departureCity.map(c => a.cityCode === c).getOrElse(slick.lifted.LiteralColumn(true))
)
aa <- slickAirports.filter(a =>
fl.arrivalAirportId === a.id &&
arrivalCity.map(c => a.cityCode === c).getOrElse(slick.lifted.LiteralColumn(true))
)
} yield (fl, sf, al, da, aa)
db.run(monadicJoin.result)
}
The output from this is a Vector containing sequences, e.g:
Vector(
(
Flight(Some(1),123,216,2013,3,1455,2540,3,905,500,1150),
ScheduledFlight(Some(1),1,2016-04-13,90,10),
Airline(Some(216),BA,BAW,British Airways,United Kingdom),
Airport(Some(2013),LHR,Heathrow,LON,...),
Airport(Some(2540),JFK,John F Kennedy Intl,NYC...)
),
(
etc ...
)
)
I'm currently rendering the JSON in the controller by calling .toJson on a Map and inserting this Vector (the results param below), like so:
flightService.search(departureCity, arrivalCity, departureDate).map(results => {
Ok(
Map[String, Any](
"status" -> "OK",
"data" -> results
).toJson
).as("application/json")
})
While this sort of works, it produces output in an unusual format; an array of results (the rows) within each result object the joins are nested inside objects with keys: "_1", "_2" and so on.
So the question is: How should I go about restructuring this?
There doesn't appear to be anything which specifically covers this sort of scenario in the Slick docs. Therefore I would be grateful for some input on what might be the best way to refactor this Vector of Seq's, with a view to renaming each of the joins or even flattening it out and only keeping certain fields?
Is this best done in the DAO search method before it's returned (by mapping it somehow?) or in the controller after I get back the Future results Vector from the search method?
Or I'm wondering whether it would be preferable to abstract this sort of mutation out somewhere else entirely, using a transformer perhaps?

Answer 1

You need JSON Reads/Writes/Format Combinators
In the first place you must have Writes[T] for all your classes (Flight, ScheduledFlight, Airline, Airport).
Simple way is using Json macros
implicit val flightWrites: Writes[Flight] = Json.writes[Flight]
implicit val scheduledFlightWrites: Writes[ScheduledFlight] = Json.writes[ScheduledFlight]
implicit val airlineWrites: Writes[Airline] = Json.writes[Airline]
implicit val airportWrites: Writes[Airport] = Json.writes[Airport]
You must implement OWrites[(Flight, ScheduledFlight, Airline, Airport, Airport)] for Vector item also. For example:
val itemWrites: OWrites[(Flight, ScheduledFlight, Airline, Airport, Airport)] = (
(__ \ "flight").write[Flight] and
(__ \ "scheduledFlight").write[ScheduledFlight] and
(__ \ "airline").write[Airline] and
(__ \ "airport1").write[Airport] and
(__ \ "airport2").write[Airport]
).tupled
for writing whole Vector as JsAray use Writes.seq[T]
val resultWrites: Writes[Seq[(Flight, ScheduledFlight, Airline, Airport, Airport)]] = Writes.seq(itemWrites)
We have all to response your data
flightService.search(departureCity, arrivalCity, departureDate).map(results =>
Ok(
Json.obj(
"status" -> "Ok",
"data" -> resultWrites.writes(results)
)
)