播放 ReactiveMongo JSON 序列化泛型

Question

我在使用 Play 2.5.x 和 ReactiveMongo Play 时遇到问题。我正在尝试创建一个通用存储库，但在将对象序列化和反序列化到数据库时遇到了严重的问题。它总是给我以下错误：No Json deserializer found for type E. Try to implement an implicit Reads or Format for this type.

这是我的通用代码：

package repositories.mongo

import javax.inject.Inject

import core.Entity
import play.modules.reactivemongo.ReactiveMongoApi
import reactivemongo.api.QueryOpts
import repositories.Repository

import scala.collection.Seq
import scala.concurrent.{ExecutionContext, Future}
import reactivemongo.play.json._
import play.api.libs.json._
import reactivemongo.play.json.collection.JSONCollection

class MongoRepository[K, E <: Entity[K]] @Inject()(reactiveMongo: ReactiveMongoApi) extends Repository[K, E] {

  protected def collection(implicit ec: ExecutionContext) = reactiveMongo.database.map(_.collection[JSONCollection](this.getCollectionName))

  protected def getCollectionName: String = {
    "users"
  }

  def getAll(count: Int, skip: Int)(implicit ec: ExecutionContext): Future[Seq[E]] = {
    this.collection.flatMap(_.find(Json.obj())
      .options(QueryOpts(skipN = skip))
      .cursor[E]().collect[Seq[E]](count))
  }

  def getFilter(count: Int, skip: Int, f: E => Boolean)(implicit ec: ExecutionContext): Future[Seq[E]] = {

    this.collection.flatMap(_.find(f)
      .options(QueryOpts(skipN = skip))
      .cursor[E]().collect[Seq[E]](count))
  }

  def getById(id: K)(implicit ec: ExecutionContext): Future[Option[E]] = {
    this.collection.flatMap(_.find(Json.obj("_id" -> id.toString)).one[E])
  }

  def create(entity: E)(implicit ec: ExecutionContext): Future[Option[E]] = {
    this.collection.flatMap(_.insert(entity)).flatMap(_ => Future.successful(Option(entity)))
  }

  def updateById(id: K, entity: E)(implicit ec: ExecutionContext): Future[Option[E]] = {
    this.collection.flatMap(_.findAndUpdate(Json.obj("_id" -> id.toString), entity)
      .map(_.result[E]))
  }

  def deleteById(id: K)(implicit ec: ExecutionContext): Future[Option[E]] = {
    this.collection.flatMap(_.findAndRemove(Json.obj("_id" -> id.toString))
      .map(_.result[E]))
  }

}

这是我的具体 class，其中包括 json 格式序列化程序。

package core

import play.api.libs.json.Json

trait Entity[K] {
  val id: K
}

case class User(
                 id: String,
                 name: String,
                 email: String
               ) extends Entity[String] {

}

object User {
  implicit val jsonFormat = Json.format[User]
}

Answer 1

当您创建 MongoRepository 时，您需要说明 E 需要 json Format。你可以这样做：

class MongoRepository[K, E <: Entity[K]: Format]

// this is the same as

class MongoRespository[K, E <: Entity[K]](implicit formatter: Format[E])

播放 ReactiveMongo JSON 序列化泛型

Play ReactiveMongo JSON Serialization Generics

scala

playframework

play-reactivemongo