Instead of using a fold sink which materializes to a Future you’ll need to use
a fold combinator which produces the result as its only value after the
substream has completed, i.e. you keep the computation results within the
streaming domain a bit longer instead of going to the Future domain
immediately. Your 1.0 solution must have done something very similar, only with
a different API (i.e. you folded the substreams and then probably used mapAsync
to flatten the resulting stream of Futures).
Regards,
Roland
> 26 apr 2016 kl. 18:05 skrev Debasish Ghosh <ghosh.debas...@gmail.com>:
>
> Roland -
>
> I need to merge into a fold sink w/ a Monoid. Consider the following example
> ..
>
> case class Transaction(id: String, accountNo: String, debitCredit:
> TransactionType, amount: Amount, date: Date = today)
>
> and I have the following list of Transactions ..
>
> val txns =
> Seq(
> Transaction("t-1", "a-1", Debit, 1000),
> Transaction("t-2", "a-2", Debit, 1000),
> Transaction("t-3", "a-3", Credit, 1000),
> Transaction("t-4", "a-1", Credit, 1000),
> Transaction("t-5", "a-1", Debit, 1000),
> Transaction("t-6", "a-2", Debit, 1000),
> Transaction("t-7", "a-3", Credit, 1000),
> Transaction("t-8", "a-3", Debit, 1000),
> Transaction("t-9", "a-2", Credit, 1000),
> Transaction("t-10", "a-2", Debit, 1000),
> Transaction("t-11", "a-1", Credit, 1000),
> Transaction("t-12", "a-3", Debit, 1000)
> )
>
> I do a group by accountNo, which gives me 3 substreams. Each substream needs
> to go into a fold sink where I fold using a Monoid. The Monoid has the logic
> of merging transactions belonging to the same accountNo. The logic that u
> suggest will not do this. I need to access the substreams separately. That's
> why I did a groupBy (similar to SQL groupBy). And I could do this in the 1.0
> version.
>
> Any workaround that u suggest ?
>
> Thanks.
>
> On Tue, Apr 26, 2016 at 9:18 PM, Roland Kuhn <goo...@rkuhn.info
> <mailto:goo...@rkuhn.info>> wrote:
> If you need the results from the substreams you’ll have to merge them back
> into the mainstream and aggregate them there:
>
> transactions.groupBy(100,
> ...).fold(...).mergeSubstreams.grouped(100).to(Sink.head)
>
> Regards,
>
> Roland
>
>> 26 apr 2016 kl. 17:36 skrev debasish <ghosh.debas...@gmail.com
>> <mailto:ghosh.debas...@gmail.com>>:
>>
>> Viktor -
>>
>> Here's the same stuff that works for akka-streams version
>> akka-stream-experimental 1.0 RC4. ..
>> https://gist.github.com/debasishg/4d596c1f26d4759ed65e281bb2e6fd2c
>> <https://gist.github.com/debasishg/4d596c1f26d4759ed65e281bb2e6fd2c> ..
>>
>> The upgrade that I am having trouble with is defining netTxn (pls see the
>> gist). The groupBy works like a charm in the older version. But in the newer
>> version it returns a Subflow and I was stumped how to get hold of each of
>> the substreams and fold them using a Monoid on a fold sink. Konrad's
>> solution was to use the to method of subflow. But somehow it's not giving
>> the desired result .. help ?
>>
>> Thanks.
>>
>>
>> On Tuesday, April 26, 2016 at 8:46:11 PM UTC+5:30, √ wrote:
>> What are you expecting to be returned?
>>
>> --
>> Cheers,
>> √
>>
>> On Apr 26, 2016 3:49 PM, "Debasish Ghosh" <ghosh.d...@gmail.com <>> wrote:
>> Thanks Konrad for the pointer .. when I run the graph I get a NotUsed ..
>> That's not hwat I get with the earlier implementation. Please have a look at
>> the gist ..
>> https://gist.github.com/debasishg/a42e867bb2bc8ad18243597178bbce93
>> <https://gist.github.com/debasishg/a42e867bb2bc8ad18243597178bbce93> .. what
>> am I doing wrong.
>>
>> Thanks.
>>
>> On Tue, Apr 26, 2016 at 6:22 PM, Konrad Malawski <konrad....@typesafe.com
>> <>> wrote:
>> (I did a quick mock Transaction type, your Monoid should work fine there
>> ofc).
>>
>> -- Konrad
>>
>> On Sunday, 24 April 2016 21:42:43 UTC+2, debasish wrote:
>> Hi -
>>
>> I am trying to migrate some akka-streams code from an earlier version
>> (akka-stream-experimental 1.0.RC4) .. please have a look at the following ..
>>
>> /**
>> * Create multiple streams out of a single stream. The stream "transactions"
>> is being
>> * demultiplexed into many streams split by account number. Each of the
>> sub-streams are
>> * then materialized to the fold sink "txnSink", which folds each of the
>> transaction
>> * substreams to compute the net value of the transaction for that account
>> */
>> val netTxn: Source[RunnableGraph[Future[Transaction]], Unit] =
>> transactions.map(validate).groupBy(_.accountNo).map { case (a, s) =>
>> s.toMat(txnSink)(Keep.right) }
>>
>> I am trying to create substreams based on a field accountNo within a
>> Transaction. Then I pass each substream to toMat with a Sink which is a fold
>> Sink defined as below ..
>>
>> /**
>> * Would like to fold transactions through monoid append
>> */
>> val txnSink: Sink[Transaction, Future[Transaction]] =
>> Sink.fold[Transaction, Transaction](TransactionMonoid.zero)(_ |+| _)
>>
>> The idea is to apply a monoid over each substream and do some netting on
>> transactions belonging to the same accountNo.
>>
>> How can I migrate this to 2.4.4 ? Now groupBy returns a Subflow and I am not
>> sure how to apply each of the substreams to the materializer. One option
>> that works will be to create a Map[String, Transaction] upfront and then
>> directly apply the monoid to the Map in the main stream and not create any
>> substream. But I would like to have the substreams fro some other purpose as
>> well.
>>
>> Any help will be appreciated ..
>>
>> Regards.
>> - Debasish
>>
>>
>>
>>
>>
>> --
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>>
>> --
>> Debasish Ghosh
>> http://manning.com/ghosh2 <http://manning.com/ghosh2>
>> http://manning.com/ghosh <http://manning.com/ghosh>
>>
>> Twttr: @debasishg
>> Blog: http://debasishg.blogspot.com <http://debasishg.blogspot.com/>
>> Code: http://github.com/debasishg <http://github.com/debasishg>
>>
>> --
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> --
> Debasish Ghosh
> http://manning.com/ghosh2 <http://manning.com/ghosh2>
> http://manning.com/ghosh <http://manning.com/ghosh>
>
> Twttr: @debasishg
> Blog: http://debasishg.blogspot.com <http://debasishg.blogspot.com/>
> Code: http://github.com/debasishg <http://github.com/debasishg>
>
> --
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