Play Framework: How to serialize/deserialize an enumeration to/from JSON

Question

Given the following enumeration...

object MyEnum extends Enumeration {

  type MyEnum = Value

  val Val1 = Value("val1")
  val Val2 = Value("val2")
  val ValN = Value("valN")

  implicit val myEnumFormat = new Format[MyEnum] {
    def reads(json: JsValue) = MyEnum.withName(json.as[String].value) // doesn't compile
    def writes(myEnum: MyEnum) = JsString(myEnum.toString)
  }
}

... I need to serialize/deserialize it to/from JSON. myEnumFormat does not compile and I always get the following error message:

type mismatch;
[error]  found   : models.MyEnum.Value
[error]  required: play.api.libs.json.JsResult[models.MyEnumValue]
[error]  Note: implicit value myEnumFormat is not applicable here because it comes after the application point and it lacks an explicit result type
[error]     def reads(json: JsValue) = MyEnum.withName(json.as[JsString].value)

Am I missing something?

score 34 · Answer 1 · answered Apr 15 '16 at 02:57

34

implicit val genderReads = Reads.enumNameReads(Gender) is working fine for me. Play Scala 2.4.2

answered Apr 15 '16 at 02:57

surenyonjan

2,097
3
17
26

score 17 · Accepted Answer · answered May 22 '14 at 21:04

17

Try changing it to

def reads(json: JsValue) = JsSuccess(MyEnum.withName(json.as[String].value))

answered May 22 '14 at 21:04

Artur Nowak

5,254
3
22
32

It is not a good approach. If json is JsNull, ```json.as[String]```will throw an exception. – ClassNotFoundException Oct 30 '19 at 13:17

score 15 · Answer 3 · answered Feb 14 '18 at 14:05

Expanding on @surenyonjan's response, the following works nicely with Play Json 2.6:

object MyEnum extends Enumeration {
  type MyEnum = Value
  val e1, e2 = Value

  implicit val myEnumReads = Reads.enumNameReads(MyEnum)
  implicit val myEnumWrites = Writes.enumNameWrites
}

Andrii Abramov · Answer 4 · 2023-07-04T13:37:37.223

13

Play 2.7+

Since play-json 2.7 there is a Json.formatEnum method. Added in scope of #140

Example:

object MyEnum extends Enumeration {
  type MyEnum = Value

  val Val1 = Value("val1")
  val Val2 = Value("val2")
  val ValN = Value("valN")

  implicit val format: Format[MyEnum] = Json.formatEnum(this)
}

edited Jul 04 '23 at 13:37

answered Jul 02 '19 at 06:41

Andrii Abramov

10,019
9
74
96

2

This should be the correct answer now. – Aiono Oct 06 '21 at 16:55

score 3 · Answer 5 · answered Sep 14 '15 at 14:42

3

I have put together more generic and re-usable EnumerationReads, EnumerationWrites and EnumerationFormat classes and have posted them on my github page:

EnumerationCombinators.scala

answered Sep 14 '15 at 14:42

Rushing

126
4

Play Framework: How to serialize/deserialize an enumeration to/from JSON

5 Answers5

Play 2.7+

Linked