toGist

  case class Person(firstname: String, lastname: String)

  type MongoReader[T] = MongoDBObject => T
  type MongoWriter[T] = T => MongoDBObject

  def readArray[T : MongoReader](name: String) = new MongoReader[List[T]] {
    def apply(dbo: MongoDBObject) = {
      println("dbo = %s".format(dbo.toString))
      println("dbo.%s = %s".format(name, dbo.as[BasicDBList](name).toString))
      dbo.as[BasicDBList](name).map { e => 
        implicitly[MongoReader[T]].apply(e.asInstanceOf[DBObject])
      }.toList
    }
  }

  def writeArray[T : MongoWriter](name: String, dbo: MongoDBObject) = new MongoWriter[List[T]] {
    def apply(xs: List[T]) = dbo += (name ->
      xs.map { e => implicitly[MongoWriter[T]].apply(e) }.toList)
  }

  implicit object PersonWriter extends MongoWriter[Person] {
    def apply(p: Person) = MongoDBObject(
      "firstname" -> p.firstname,
      "lastname" -> p.lastname)
  }
  implicit object PersonReader extends MongoReader[Person] {
    def apply(dbo: MongoDBObject) =
      Person(dbo.as[String]("firstname"), dbo.as[String]("lastname"))
  }

scala> readArray[Person]("people").apply(writeArray[Person]("people", MongoDBObject()).apply(xs))
23:21:31.080 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Registering Scala Conversions.
23:21:31.086 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Deserializers for Scala Conversions registering
23:21:31.087 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Serializers for Scala Conversions registering
23:21:31.088 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up OptionSerializer
23:21:31.093 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up ScalaJCollectionSerializer
23:21:31.100 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up ScalaRegexSerializers
23:21:31.102 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Hooking up scala.util.matching.Regex serializer
23:21:31.103 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Reached base registration method on MongoConversionHelper.
23:21:31.162 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Registering Scala Conversions.
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Deserializers for Scala Conversions registering
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Serializers for Scala Conversions registering
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up OptionSerializer
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up ScalaJCollectionSerializer
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Setting up ScalaRegexSerializers
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Hooking up scala.util.matching.Regex serializer
23:21:31.163 [run-main] DEBUG c.m.c.c.c.s.RegisterConversionHelpers$ - Reached base registration method on MongoConversionHelper.
dbo = Map(people -> List(Map(firstname -> me, lastname -> myself), Map(firstname -> you, lastname -> yourself)))
java.lang.ClassCastException: scala.collection.immutable.$colon$colon cannot be cast to com.mongodb.BasicDBList
        at anima.casbah.MongoUtils$Bindings$$anon$4.apply(CasbahDomain.scala:310)
        at anima.casbah.MongoUtils$Bindings$$anon$4.apply(CasbahDomain.scala:307)
        at .<init>(<console>:24)
        at .<clinit>(<console>)
        at .<init>(<console>:11)
        at .<clinit>(<console>)
        at $print(<console>)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.call(IMain.scala:704)
        at scala.tools.nsc.interpreter.IMain$Request.loadAndRun(IMain.scala:914)
        at scala.tools.nsc.interpreter.IMain.loadAndRunReq$1(IMain.scala:546)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:577)
        at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:543)
        at scala.tools.nsc.interpreter.ILoop.reallyInterpret$1(ILoop.scala:694)
        at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:745)
        at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:651)
        at scala.tools.nsc.interpreter.ILoop.processLine$1(ILoop.scala:542)
        at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:550)
        at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:822)
        at scala.tools.nsc.interpreter.ILoop.main(ILoop.scala:851)
        at xsbt.ConsoleInterface.run(ConsoleInterface.scala:51)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sbt.compiler.AnalyzingCompiler.call(AnalyzingCompiler.scala:57)
        at sbt.compiler.AnalyzingCompiler.console(AnalyzingCompiler.scala:48)
        at sbt.Console.console0$1(Console.scala:23)
        at sbt.Console$$anonfun$apply$2$$anonfun$apply$1.apply$mcV$sp(Console.scala:24)
        at sbt.TrapExit$.executeMain$1(TrapExit.scala:33)
        at sbt.TrapExit$$anon$1.run(TrapExit.scala:42)