I thought I needed to use a GraphStageLogic because I need to do the
following:
request url for page of data and push
if response has next token, grab another page and push
continue until no next token
complete the stream
I wasn't sure how to accomplish that logic in a Source.
I figured out a solution by using getAsyncCallback
val pushCallback = getAsyncCallback[Seq[String]] { seq =>
push(out, seq)
}
Then on my future callback I call pushCallback.invoke(seq)
It seems to work just fine but not sure that materializing a source in a
GraphStageLogic is the best approach.
If you have some example you can point me at I'm all ears!
On Friday, December 9, 2016 at 1:27:31 AM UTC-7, drewhk wrote:
>
>
>
> On Thu, Dec 8, 2016 at 9:21 PM, <sub...@gmail.com <javascript:>> wrote:
>
>> Hi,
>>
>> I'm creating a Source via GraphStageLogic which makes calls to another
>> api, which happens to return a Source. However I'm unsure how to deal with
>> Source/Futures in a GraphStageLogic. It seems that I want my shape to look
>> like
>>
>> val shape: SourceShape[Seq[String]] = SourceShape(out)
>>
>>
>> but I get back a Source[ByteString, NotUsed] which I can covert to
>> Future[Seq[String]]
>> via runWith(Sink.seq). So should I make my shape
>>
>> val shape: SourceShape[Future[Seq[String]]] = SourceShape(out)
>>
>>
>> But then I need to materialize the Source inside the onPull(), which
>> doesn't seem right. Is there a better way to handle this situation?
>>
>
> You likely need to combine your stage with a flatMapConcat(). Remember
> that you don't need to implement all your logic inside a GraphStage, you
> can create Sources just by using existing combinators like mapAsync or
> flatMapConcat. In fact, if you need some custom operation that is not
> covered by the built-in combinators, it is usually a good idea to minimize
> the custom part and combine it with the existing combinators to achieve
> what you want.
>
>
>>
>> Thanks!
>>
>> --
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