升级到ReactiveMongo 0.12.RC3时类型不匹配

Question

我目前升级到0.12.RC3,希望能解决我遇到的以下问题.升级后,我收到了该collect方法的弃用警告.

所以我离开了:

def find(query: JsObject = Json.obj())(implicit reader: Reads[T]): Future[List[T]] = {
    collection.flatMap(_.find(query).cursor[T](ReadPreference.nearest).collect[List]())
}

至:

def find(query: JsObject = Json.obj())(implicit reader: Reads[T]): Future[List[T]] = {
    collection.flatMap(_.find(query).cursor[T](ReadPreference.nearest).collect[List](Int.MaxValue, Cursor.FailOnError()))
}

但是,遗憾的是我收到以下错误:

类型不匹配,预期:(​​JSONCollection)=> Future [NotInferedS],actual:(JSONCollection)=> Any

Answer 1

我认为你缺少一些编译器消息,应该看到类似的东西:

  (maxDocs: Int,stopOnError: Boolean)(implicit cbf: scala.collection.generic.CanBuildFrom[List[_],T,List[T]], implicit ec: scala.concurrent.ExecutionContext)scala.concurrent.Future[List[T]] <and>
  (maxDocs: Int,err: reactivemongo.api.Cursor.ErrorHandler[List[T]])(implicit cbf: scala.collection.generic.CanBuildFrom[List[_],T,List[T]], implicit ec: scala.concurrent.ExecutionContext)scala.concurrent.Future[List[T]]
 cannot be applied to (Int, reactivemongo.api.Cursor.ErrorHandler[Any])
Error occurred in an application involving default arguments.
           collection.flatMap(_.find(query).cursor[T](ReadPreference.nearest).collect[List](Int.MaxValue, Cursor.FailOnError()))

这意味着在这种情况下,如果要使用new collect而不是已弃用的,则需要使用结果类型正确地注释ErrorHandler(there FailOnError):FailOnError[List[T]]

def find(query: JsObject = Json.obj())(implicit reader: Reads[T]): Future[List[T]] = collection.flatMap(_.find(query).cursor[T](ReadPreference.nearest).collect[List](Int.MaxValue, Cursor.FailOnError[List[T]]()))