CODEWITHSUNDEEP
jsonscalaplayframework
j3d
j3d

Reputation: 9734

Validating JSON with Play: How to generate possible missing data

Given the following Reads that validates the JSON representation of an user...

val userValidator: Reads[JsValue] = (
  (__ \ 'id).readNullable[Int] ~ // how do I invoke Random.nextInt if 'id is missing?
  (__ \ 'name).read[String]
).tupled ~> implicitly[Reads[JsValue]]

... how do I generate the id key if not specified in the input JSON? Let's suppose the input JSON is something like this:

{
  "name": "Joe
}

How do I add the id key and generate its value with Random.nextInt, so that the resulting JSON is something like this?

{
  "id": 153876748,
  "name": "Joe"
}

Upvotes: 1

Views: 122

Answers (1)

Jean
Jean

Reputation: 21595

In my projects, I have defined the following method :

def withDefault[A](key: String, default: =>A)(implicit writes: Writes[A]) = 
    __.json.update((__ \ key).json.copyFrom((__ \ key).json.pick orElse Reads.pure(Json.toJson(default))))

Then you can write :

  val _userValidator = (
    (__ \ 'id).readNullable[Int] ~
      (__ \ 'name).read[String]
    ).tupled  ~> implicitly[Reads[JsValue]]
  val userValidator = _userValidator.compose(withDefault("id",Random.nextInt ))

Which should do what you asked :

scala> userValidator.reads(Json.parse("""{"name": "Joe"}"""))
res6: play.api.libs.json.JsResult[play.api.libs.json.JsValue] = JsSuccess({"name":"Joe","id":721872039},)

Upvotes: 2

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