Constant value in Scala Play JSON Reads

Question

I'd like to use a constant value when constructing an object via a JSON read.

For example the class would be:

case class UserInfo(
  userId: Long = -1, 
  firstName: Option[String] = None,
  lastName:  Option[String] = None
)

And the read would be:

   implicit val userRead: Reads[UserInfo] = (
      (JsPath \ "userId").read[Long] and
      (JsPath \ "firstName").readNullable[String] and
      (JsPath \ "lastName").readNullable[String] 
    )(UserInfo.apply _)

But I don't want to have to specify the value for userId in the JSON object. How would I go about coding the Reads so that the value of -1 is always created in the UserInfo object without specifying it in the JSON object being read?

Michael Zajac · Accepted Answer · 2014-10-15T15:36:15.927

11

Use Reads.pure

implicit val userRead: Reads[UserInfo] = (
  Reads.pure(-1L) and
  (JsPath \ "firstName").readNullable[String] and
  (JsPath \ "lastName").readNullable[String] 
)(UserInfo.apply _)

edited Oct 15 '14 at 15:36

answered Oct 15 '14 at 14:47

Michael Zajac

55,144
7
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score 0 · Answer 2 · answered Oct 15 '14 at 15:22

0

Thanks!

I had to make one minor change to force it to a Long:

implicit val userRead: Reads[UserInfo] = (
  Reads.pure(-1:Long) and
  (JsPath \ "firstName").readNullable[String] and
  (JsPath \ "lastName").readNullable[String] 
)(UserInfo.apply _)

answered Oct 15 '14 at 15:22

ccudmore

193
1
7

Constant value in Scala Play JSON Reads

2 Answers2