Question

我正在使用reactivemongo-akka-stream并尝试转换AkkaStreamCursor.documentSource。我正在看到两个问题：

documentation表示此操作返回Source[T, NotUsed]但collection.find(query).cursor[BSONDocument].doccumentSource()返回Source[BSONDocument, Future[State]]。有没有办法避免State对象？

假设我使用Future[State]我希望得到以下类的来源

case class Inner(foo: String, baz: Int)

case class Outer(bar: Inner)

//
implicit object InnerReader extends BSONDocumentReader[Inner]//defined

val getCollection: Future[BSONCollection] = connection.database("db").map(_.collection("things")

def stream()(implicit m: Materializer): Source[Outer, Future[State]] = {
 getCollection.map(_.find().cursor[Inner]().documentSource()).map(_.via(Flow[Inner].map(in => Outer(in))))

但是我没有找回我可以处理的Future[Source[Outer, Future[State]]，而是返回Future[Source[Inner, Future[State]]#Repr[Outer]]

如何将bson读者与此库一起使用？

Answer 1

根据cchantep的建议，我需要将fromFuture与flatMapConcat一起使用：

def stream()(implicit m: Materializer): Source[Outer, NotUsed] = {
 val foo = getCollection.map(x => col2Source(x))

 fix(foo).via(flowmap(map = Outer(_)))
}
def col2Source(col: BSONCollection): Source[Inner, Future[State]] = {
 val cursor: AkkaStreamCursor[Inner] = 
   col.find(BSONDocument.empty).cursor[Inner]()

 cursor.documentSource()
}

def flowmap[In, Out](
 map: (In) => Out
): Flow[In, Out, NotUsed] = Flow[In].map(e => map(e))

def fix[Out, Mat](futureSource: Future[Source[Out, Mat]]): Source[Out, NotUsed] = {
 Source.fromFuture(futureSource).flatMapConcat(identity)
}

ReactiveMongo与Akka Streams自定义来源

1 个答案: