Question

我有一个这样的案例类：

case class Product(ean: Long, name: String, description: String, purchasePrice: Option[BigDecimal] = None, sellingPrice: Option[BigDecimal] = None)

我有一个非隐式的写作：

val adminProductWrites = (
  (JsPath \ "ean").write[Long] and
  (JsPath \ "name").write[String] and
  (JsPath \ "description").write[String] and
  (JsPath \ "purchase_price").writeNullable[BigDecimal] and
  (JsPath \ "selling_price").writeNullable[BigDecimal]
)(unlift(Product.unapply))

然后我有一个Option [Product]实例：

val prod = Some(Product(5018206244611L, "Zebra Paperclips", "Zebra Length 28mm Assorted 150 Pack"))

当我尝试序列化时......：

val jsonStr = Json.toJson(prod) (adminProductWrites)

我收到了这样的错误：

<console>:21: error: type mismatch;
 found   : play.api.libs.json.OWrites[Product]
 required: play.api.libs.json.Writes[Some[Product]]
       val jsonStr = Json.toJson(prod) (adminProductWrites)

所以，首先（仅供比较）我试过这个：

 val jsonStr = Json.toJson(prod.get) (adminProductWrites)

有效：

jsonStr: play.api.libs.json.JsValue = {"ean":5018206244611,"name":"Zebra Paperclips","description":"Zebra Length 28mm Assorted 150 Pack"}

但我不想那样做（打电话给.get）。当Writes声明为隐式时，我需要按照它的方式工作：

implicit object ProductWrites extends Writes[Product] {
  def writes(p: Product) = Json.obj(
    "ean" -> Json.toJson(p.ean),
    "name" -> Json.toJson(p.name),
    "description" -> Json.toJson(p.description)
  )
}

（使用隐式Writes，此行有效）：

scala> val jsonStr = Json.toJson(prod)
jsonStr: play.api.libs.json.JsValue = {"ean":5018206244611,"name":"Zebra Paperclips","description":"Zebra Length 28mm Assorted 150 Pack"}

我错过了什么？

附加说明：

我的隐含写作不完整，我故意删除了最后2个字段（purchasePrice和sellingPrice）。原因是：这段代码没有编译：

implicit object ProductWrites extends Writes[Product] {
  def writes(p: Product) = Json.obj(
    "ean" -> Json.toJson(p.ean),
    "name" -> Json.toJson(p.name),
    "description" -> Json.toJson(p.description),
    "purchase_price" -> p.purchasePrice.getOrElse(None),
    "selling_price" -> p.sellingPrice.getOrElse(None)
  )

}

我给出了这个错误：

<console>:24: error: No Json serializer found for type Serializable. Try to implement an implicit Writes or Format for this type.
       "purchase_price" -> Json.toJson(p.purchasePrice.getOrElse(None)),

提前致谢，拉嘎

Answer 1

您的代码有两个问题：

prod的类型为Some[Product]。使用val prod: Option[Product] = ...
您必须使用Option-Writes：Json.toJson(prod)(Writes.OptionWrites(adminProductWrites))。如果使用隐式Writes，则编译器的代码产品完全相同（也使用OptionWrites）。


    scala> val prod: Option[Product] = Some(Product(5018206244611L, "Zebra Paperclips", "Zebra Length 28mm Assorted 150 Pack"))
        prod: Option[Product] = Some(Product(5018206244611,Zebra Paperclips,Zebra Length 28mm Assorted 150 Pack,None,None))

    scala> Json.toJson(prod)(Writes.OptionWrites(adminProductWrites))
        res2: play.api.libs.json.JsValue = {"ean":5018206244611,"name":"Zebra Paperclips","description":"Zebra Length 28mm Assorted 150 Pack"}

    scala> val prod: Option[Product] = None
        prod: Option[Product] = None

    scala> Json.toJson(prod)(Writes.OptionWrites(adminProductWrites))
        res3: play.api.libs.json.JsValue = null

非隐式写入不能处理Option（Scala，JSON，Play 2.3.6）

1 个答案: