Reading and Writing in Scala Playing Back Lists of Custom Classes

Question

So I have two classes in my project

case class Item(id: Int, name: String)

and

case class Order(id: Int, items: List[Item])

I try to read and write properties for Order, but I get a compiler error:

"Unapply or unapplySeq function not found"

In my controller, I have the following:

implicit val itemReads = Json.reads[Item]
implicit val itemWrites = Json.writes[Item]
implicit val listItemReads = Json.reads[List[Item]]
implicit val listItemWrites = Json.writes[List[Item]]

The code works for itemReadsand itemWrites, but not for the bottom two. Can someone tell me where I'm wrong, I'm new to the Play platform.

Thank you for your time.

Answer 1

The error " No unapply or unapplySeq function found" is caused by these two:

implicit val listItemReads = Json.reads[List[Item]]
implicit val listItemWrites = Json.writes[List[Item]]

Just throw them away. As Ende said , Play knows how to deal with lists.

Reads Writes Order ! , Format, Reads Writes, :

case class Item(id: Int, name: String)

object Item {
  implicit val format = Json.format[Item]
}

case class Order(id: Int, items: List[Item])

object Order {
  implicit val format = Json.format[Order]
}

; Item, - Order.

, , . , , - .

Answer 2

, , :

scala> import play.api.libs.json._ 
import play.api.libs.json._

scala>   case class Item(id: Int, name: String)
defined class Item

scala>   case class Order(id: Int, items: List[Item])
defined class Order

scala>   implicit val itemReads = Json.reads[Item]
itemReads: play.api.libs.json.Reads[Item] = play.api.libs.json.Reads$$anon$8@478fdbc9

scala>   implicit val itemWrites = Json.writes[Item]
itemWrites: play.api.libs.json.OWrites[Item] = play.api.libs.json.OWrites$$anon$2@26de09b8

scala>   Json.toJson(List(Item(1, ""), Item(2, "")))
res0: play.api.libs.json.JsValue = [{"id":1,"name":""},{"id":2,"name":""}]

scala>   Json.toJson(Order(10, List(Item(1, ""), Item(2, ""))))
res1: play.api.libs.json.JsValue = {"id":10,"items":[{"id":1,"name":""},{"id":2,"name":""}]}

, - , unapply / List . play-json .

Answer 3

It works:

case class Item(id: Int, name: String)

case class Order(id: Int, items: List[Item])

implicit val itemFormat = Json.format[Item]
implicit val orderFormat: Format[Order] = (
  (JsPath \ "id").format[Int] and
    (JsPath \ "items").format[JsArray].inmap(
      (v: JsArray) => v.value.map(v => v.as[Item]).toList,
      (l: List[Item]) => JsArray(l.map(item => Json.toJson(item)))
    )
  )(Order.apply, unlift(Order.unapply))

It also allows you to configure naming for your JSON object. The following is an example of serialization in action.

Json.toJson(Order(1, List(Item(2, "Item 2"))))
res0: play.api.libs.json.JsValue = {"id":1,"items":[{"id":2,"name":"Item 2"}]}

Json.parse(
  """
    |{"id":1,"items":[{"id":2,"name":"Item 2"}]}
  """.stripMargin).as[Order]
res1: Order = Order(1,List(Item(2,Item 2)))

I would also recommend using formatinstead readand writeif you are doing symmetric serialization / deserialization.