Play Framework 2.2.x Scala JSON读取中的公共路径前缀

Question

I would like to only read "value" from the following JSON

{
  "field": "feed",
  "value": {
    "item": "post",
    "verb": "add",
    "post_id": 1234568567515,
    "sender_id": 10200718414514
  }
}

into this:

case class Value (
  item: String,
  verb: String,
  itemId: Long,
  senderId: Long
)

The Reads[Value] looks like this:

implicit val valueReads: Reads[Value] = (
  (__ \ "item").read[String] and
  (__ \ "verb").read[String] and
  (__ \ "post_id").read[Long] and
  (__ \ "sender_id").read[Long]
) ( Value )

How can I specify the common parent node "value" for all the paths in Reads without repeating it all over the place like (__ \\ "value" \\ "item"), (__ \\ "value" \\ "verb") etc.?

Answer 1

This code seems to work:

implicit val valuereads = (__ \ "value").read {
  ((__ \ "item").read[String] and
   (__ \ "verb").read[String] and
   (__ \ "post_id").read[Long] and
   (__ \ "sender_id").read[Long] 
   )(Value.apply _)  
}

Answer 2

Not sure if it is what you are looking for, but if you want skip manually writing Reads objects, you can use macros. But for that case you should have parent case class, which will have inside two fields: field and value .

So it'll be something like:

case class Value (
  item: String,
  verb: String,
  itemId: Long,
  senderId: Long
)

case class MyClass(field: String, value: Value)


implicit val myClassReads = Json.reads[MyClass]
implicit val valueReads = Json.reads[Value]

So at the end you can get your value from the MyClass object.