It is not a good practice to have such a big json with many root variables. Nevertheless, we might need to call a rest api that will give a json like this
{
"a1": ...,
"a2" : ...,
"a3" : ...,
"a4" : ...,
"a5" : ...,
"a6" : ...,
"a7" : ...,
"a8" : ...,
"a9" : ...,
"a10" : ...,
"a11" : ...,
"a12" : ...,
"a13" : ...,
"a14" : ...,
"a15" : ...,
"a16" : ...,
"a17" : ...,
"a18" : ...,
"a19" : ...,
"a20" : ...,
"a21": ...,
"a22" : ...,
"a23" : ...,
"a24" : ...,
....
}
First approach
Since scala 2.11 we can have case class with more than 22 fields, so the following compiles.
case class JsonExample (
a1:String, a2:String, a3:String, a4:String, a5:String, a6:String,
a7:String, a8:String, a9:String, a10:String, a11:String, a12:String,
a13:String, a14:String, a15:String, a16:String, a17:String, a18:String,
a19:String, a20:String, a21:String, a22:String, a23:String, a24:String
)
But if we try to use Play JSON automated mapping
import play.api.libs.json._
implicit val jsonExampleFormat = Json.format[JsonExample]
we get a compiler error
<console>:16: error: No unapply or unapplySeq function found
implicit val jsonExampleFormat = Json.format[JsonExample]
^
Instead we can use Play-Json extensions(requires play-json >= 2.4)
import ai.x.play.json.Jsonx
implicit val jsonExampleFormat = Jsonx.formatCaseClass[JsonExample]
jsonExampleFormat: play.api.libs.json.Format[JsonExample] = $anon$1@b7f7890
So now we have a Play Json format for a case class with more than 22 fields, and can use it as described in Play Json documentation
Second approach
I don’t consider having a case class with so many fields a good solution.
A better solution is to organize these fields in “logical” embedded case classes.
case class A (
a1:String, a2:String, a3:String, a4:String,
a5:String, a6:String, a7:String, a8:String
)
case class B (
a9:String, a10:String, a11:String, a12:String,
a13:String, a14:String, a15:String, a16:String
)
case class C (
a17:String, a18:String, a19:String, a20:String,
a21:String, a22:String, a23:String, a24:String
)
case class JsonExample2 (
a : A,
b : B,
c : C
)
We use a “regular” play json format for the embedded case classes.
import play.api.libs.json._
implicit val jsonAFormat : Format[A] = Json.format[A]
implicit val jsonBFormat : Format[B]= Json.format[B]
implicit val jsonCFormat : Format[C] = Json.format[C]
And the “trick” now is to use the JsPath
Play Json Combinator for the embedded case classes without any path.
import play.api.libs.functional.syntax._
implicit val jsonExample2Format: Format[JsonExample2] = (
(JsPath).format[A] and
(JsPath).format[B] and
(JsPath).format[C]
)(JsonExample2.apply, unlift(JsonExample2.unapply))
That’s all folks!