setting default values with Play! Json Combinators - json

Question

I'm using play!'s json combinators to validate, read and write JSON. Is it possible to specify default values in reads or writes if they are not set?
validation of json is done like this (where json is a JsValue):
json.validate[Pricing]
My code is:
case class Pricing(
_id: ObjectId = new ObjectId,
description: String,
timeUnit: TimeUnit.Value,
amount: Double = 0.0) {
#Persist val _version = 1
}
my reads and writes:
implicit val pricingReads: Reads[Pricing] = (
(__ \ "_id").read[ObjectId] and
(__ \ "description").read[String] and
(__ \ "timeUnit").read[TimeUnit.Value] and
(__ \ "amount").read[Double]
)(Pricing.apply _)
implicit val pricingWrites: Writes[Pricing] = (
(__ \ "_id").write[ObjectId] and
(__ \ "description").write[String] and
(__ \ "timeUnit").write[TimeUnit.Value] and
(__ \ "amount").write[Double]
)(unlift(Pricing.unapply))
so if I would recieve a Json like:
{"description": "some text", "timeUnit": "MONTH"}
I get errors, that fields _id and amount are missing. Is there any possiblity to set the default values without adding it directy to the JsValue?
Thanks in advance!

Answer 1

I'd rather use Options:
case class Pricing(
_id: Option[ObjectId],
description: String,
timeUnit: TimeUnit.Value,
amount: Option[Double]) {
#Persist val _version = 1
}
and replace your pricingReads with this:
implicit val pricingReads: Reads[Pricing] = (
(__ \ "_id").readNullable[ObjectId] and
(__ \ "description").read[String] and
(__ \ "timeUnit").read[TimeUnit.Value] and
(__ \ "amount").readNullable[Double]
)(Pricing.apply _)
Then your code will work on missing fields and yo will be able to do this:
_id.getOrElse(new ObjectId)