玩框架json写题答案

【问题标题】：playframework json write quesstion玩框架json写题
【发布时间】：2016-03-07 11:37:07
【问题描述】：

case class CustomerInfo (
    customerId: Long,
    customerName: String,
    cameAt: String,
    staffId:String,
    staffName:String
)

case class CustomerResult (
    customers:Option[Seq[CustomerInfo]] = None
){
    def toJson = Json.toJson(this)
}

implicit val customerInfoWrites: Writes[CustomerInfo] = (
        (JsPath \ "customer_id").write[Long] and
      (JsPath \ "customer_name").write[String] and
      (JsPath \ "came_at").write[String] and
      (JsPath \ "staff_id").write[String] and
        (JsPath \ "staff_name").write[String]
)(unlift(CustomerInfo.unapply))

implicit val custmerResultWrites: Writes[CustomerResult] = (
      (JsPath \ "customers").writeNullable[Seq[CustomerInfo]]
)(unlift(CustomerResult.unapply))

第二种方法是错误 custmerResultWrites，因为它只有一个 JsPath 写入。如果我在 CustomerResult 中再添加一个部分，则错误是可以的。错误：

found   : CustomersSearchResult.this.CustomerResult => Option[Seq[CustomersSearchResult.this.CustomerInfo]]
required: play.api.libs.json.Writes[Seq[CustomersSearchResult.this.CustomerInfo]]

【问题讨论】：

标签： scala playframework playframework-2.0

【解决方案1】：

一般来说，错误是由于使用combinators with a single field 造成的（有关一般解决方法，请参阅该问题的答案。）

一种方法是：

implicit val custmerResultWrites: Writes[CustomerResult] =
  (JsPath \ "customers").writeNullable[Seq[CustomerInfo]]
                        .contramap(_.customers)

如果customers 是空的，它会给你一个空对象（{}）。如果你想要一个空列表，你可以这样做：

val custmerResultWrites2: Writes[CustomerResult] =
  (JsPath \ "customers").writeNullable[Seq[CustomerInfo]].contramap {
    case CustomerResult(None) => Some(Seq.empty[CustomerInfo])
    case CustomerResult(seq) => seq
  }

这会导致：

{
  "customers" : [ ]
}

【讨论】：