parsing a Json Array in play framework JsObject

Question

I have the following Json:

{
  "web-category" : "macaroons",
  "sub-categories" : [
     { "name" : "pink" },
     { "name" : "blue" },
     { "name" : "green" }
  ]

}

I have got it in Play as a JsObject. So I can now successfully do the following:

//(o is the JsObject)

val webCat:Option[String] = (o \ "web-category").asOpt[String]

println(webCat.toString)

>> Some(macaroons)

So far, so good. But how do I access the array Json objects? I have this...

val subCats:Option[JsArray] = (o \ "sub-categories").asOpt[JsArray]

println(subCats.toString)

>> Some([{"name" : "blue"},{"name" : "green"},{"name" : "pink"}])

but what I need is to take the JsArray and get a List of all the names something like this:

List("blue", "green", "pink")

Don't know how to access the JsArray thusly.

my thanks for your help in this.

Travis Brown · Accepted Answer · 2014-02-26 15:34:47Z

I'd argue that it's generally a good idea to move from JSON-land to native-Scala-representation-land as early as possible. If obj is your JsObject, for example, you can write this:

val subCategories = (obj \ "sub-categories").as[List[Map[String, String]]]

val names = subCategories.map(_("name"))

Or even:

case class Category(name: String, subs: List[String])

import play.api.libs.functional.syntax._

implicit val categoryReader = (
  (__ \ "web-category").read[String] and
  (__ \ "sub-categories").read[List[Map[String, String]]].map(_.map(_("name")))
)(Category)

And then:

obj.as[Category]

This latter approach makes error handling even cleaner (e.g. you can just replace as with asOpt at this top level) and composes nicely with other Reads type class instances—if you have a JsArray of these objects, for example, you can just write array.as[List[Category]] and get what you expect.

johanandren · Accepted Answer · 2014-02-26 15:14:40Z

12

What Peter said, or:

(o \ "sub-categories" \\ "name").map(_.as[String]).toList

answered Feb 26, 2014 at 15:14

johanandren

11.5k1 gold badge27 silver badges31 bronze badges

1 Comment

Zuriar Over a year ago

Edit no I don't, my bad. I used 'sub-category' in actual fact, not 'sub-categories. Thanks for your help!

user908853 · Accepted Answer · 2014-02-26 15:13:06Z

4

Something like this:

subCats.map( jsarray => jsarray.value.map(jsvalue => (jsvalue \ "name").as[String]).toList)

This will normally return a Option[List[String]]

answered Feb 26, 2014 at 15:13

user908853

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