从 ObjectId 到案例类 BSONObjectID 的 ReactiveMongo 映射答案

【问题标题】：ReactiveMongo mapping from ObjectId to case class BSONObjectID从 ObjectId 到案例类 BSONObjectID 的 ReactiveMongo 映射
【发布时间】：2015-03-09 10:13:11
【问题描述】：

我是 Scala 和 Play 的新手，我正在尝试将 Scala BSONObjectID 映射到 mongo ObjectId。我从互联网上获得了许多样本，但仍然陷入一个编译时错误。以下是我的案例类的代码：

case class UserDetail(
 val _id: Option[BSONObjectID],
 val name: String,
 val age: Double,
 var created: Option[Long]
)  

object UserDetail{
 implicit val userDetailReads: Reads[UserDetail] = (
 (JsPath \ "_id").readNullable[BSONObjectID] and
 (JsPath \ "name").read[String] and
 (JsPath \ "age").read[Double] and
 (JsPath \ "created").readNullable[Long]
)(UserDetail.apply _)

implicit val userDetailWrites: Writes[UserDetail] = (
(JsPath \ "_id").writeNullable[BSONObjectID]and
(JsPath \ "name").write[String] and
(JsPath \ "age").write[Double] and
(JsPath \ "created").writeNullable[Long]
)(unlift { UserDetail.unapply })}

这个(JsPath \ "_id").readNullable[BSONObjectID]产生编译时错误如下：

not enough arguments for method readNullable: (implicit r: play.api.libs.json.Reads[reactivemongo.bson.BSONObjectID])play.api.libs.json.Reads[Option[reactivemongo.bson.BSONObjectID]]. Unspecified value parameter r.
not enough arguments for method readNullable: (implicit r: play.api.libs.json.Reads[reactivemongo.bson.BSONObjectID])play.api.libs.json.Reads[Option[reactivemongo.bson.BSONObjectID]]. Unspecified value parameter r.

这个(JsPath \ "_id").writeNullable[BSONObjectID] 也会产生同样的错误。

我想格式化我的 json 请求。所以我使用自定义格式化程序如下：

object BSONObjectIDFormat extends Format[BSONObjectID]{

 def writes(objectId: BSONObjectID): JsValue = JsString(objectId.toString())

 def reads(json: JsValue): JsResult[BSONObjectID] = json match {
  case JsString(x) => {
  val maybeOID: Try[BSONObjectID] = BSONObjectID.parse(x)
  if(maybeOID.isSuccess) JsSuccess(maybeOID.get) else {
    JsError("Expected BSONObjectID as JsString")
  }
}
case _ => JsError("Expected BSONObjectID as JsString")
}}

我的Json请求如下：

{
"_id":{"$oid":"54fd4b7084071e6a6ab13cee"},
"name" : "Akka",
"age" : 30,
"created" : 1425886070013
}

当我发送 JSON 请求时，出现以下错误：

[error] D:\play_projects\scala_play_sample\app\models\UserDetail.scala:35: No Js
on deserializer found for type reactivemongo.bson.BSONObjectID. Try to implement
an implicit Reads or Format for this type.
[error]     (JsPath \ "_id").readNullable[BSONObjectID] and
[error]                                  ^
[error] D:\play_projects\scala_play_sample\app\models\UserDetail.scala:42: No Js
on serializer found for type reactivemongo.bson.BSONObjectID. Try to implement a
n implicit Writes or Format for this type.
[error]     (JsPath \ "_id").writeNullable[BSONObjectID]and

【问题讨论】：

标签： scala playframework-2.3 play-reactivemongo

【解决方案1】：

在这种情况下，我们只需在 Case 类中初始化我们的自定义格式化程序。我不确定，为什么播放不自动 pic 格式。现在代码如下：

case class UserDetail(
 val _id: Option[BSONObjectID],
 val name: String,
 val age: Double,
 var created: Option[Long]
)  

object UserDetail{

 implicit val idFormatter = BSONObjectIDFormat

 implicit val userDetailReads: Reads[UserDetail] = (
 (JsPath \ "_id").readNullable[BSONObjectID] and
 (JsPath \ "name").read[String] and
 (JsPath \ "age").read[Double] and
 (JsPath \ "created").readNullable[Long]
)(UserDetail.apply _)

 implicit val userDetailWrites: Writes[UserDetail] = (
 (JsPath \ "_id").writeNullable[BSONObjectID]and
 (JsPath \ "name").write[String] and
 (JsPath \ "age").write[Double] and
 (JsPath \ "created").writeNullable[Long]
 )(unlift { UserDetail.unapply })}

【讨论】：

通常不建议在模型的案例类中使用 BSON 特定类型。它将应用模型的定义与底层持久性库的详细实现联系起来。
Hello @cchantep 而不是 BSON 特定类型。我们需要使用什么？因为当我使用 String 类型时，我无法进行诸如 find by id 之类的查询。

【解决方案2】：

对于 reactivemongo 1.0.7，将 ObjectId 映射到案例类非常容易。

Reads 和 Macros 对于大多数情况来说已经足够了。

import reactivemongo.api.bson.Macros.Annotations.{Key, Reader}
import reactivemongo.api.bson.{BSONDocumentHandler, BSONObjectID, BSONReader, Macros}

object Model {
  val idReader: BSONReader[String] = BSONReader.collect[String] { case id @ BSONObjectID(_) =>
    id.asInstanceOf[BSONObjectID].stringify
  }

  case class Post(@Reader(idReader) @Key("_id") id: String, title: String, content: String, created: Long)

  implicit val postHandler: BSONDocumentHandler[Post] = Macros.handler[Post]
}

【讨论】：