使用Play設置默認值！ Json Combinators

Question

我使用play！的json組合器來驗證，讀取和寫入JSON。如果它們沒有設置，是否可以在讀取或寫入中指定默認值？ JSON的

驗證這樣的（其中JSON是一種JsValue）來完成：

json.validate[Pricing] 

我的代碼是：

case class Pricing(
    _id: ObjectId = new ObjectId, 
    description: String, 
    timeUnit: TimeUnit.Value, 
    amount: Double = 0.0) { 
     @Persist val _version = 1 
} 

我的讀取和寫入：

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)) 

所以如果我會收到像Json：

{"description": "some text", "timeUnit": "MONTH"} 

我收到錯誤，該字段缺少_id和amount。有沒有可能在不將它直接添加到JsValue的情況下設置默認值？

在此先感謝！

Answer 1

我寧願使用Option S：

case class Pricing(
    _id: Option[ObjectId], 
    description: String, 
    timeUnit: TimeUnit.Value, 
    amount: Option[Double]) { 
     @Persist val _version = 1 
    } 

並更換pricingReads這個：

implicit val pricingReads: Reads[Pricing] = (
    (__ \ "_id").readNullable[ObjectId] and 
    (__ \ "description").read[String] and 
    (__ \ "timeUnit").read[TimeUnit.Value] and 
    (__ \ "amount").readNullable[Double] 
)(Pricing.apply _) 

那麼你的代碼將在丟失下地幹活喲就能做到這一點：

_id.getOrElse(new ObjectId)