Hi Miguel, > Is there a way to force the behavior I need, meaning... using left join and a JoinWindows output only one message (A,B) or (A, null)
I think you can try to achieve it by using *KStream-GlobalKTable left join*, where the GlobalKTable should read all records at the right topic, and then doing the left join operation. This should then output either (A,B), or (A, null). Thank you. Luke On Tue, Nov 30, 2021 at 1:23 AM Miguel González <miguel.gonza...@klar.mx> wrote: > Hello > > I have been developing a Kafka Streams app that takes as input two topics > as KStreams, processes them in some way and joins them and sends the > combined message to an output topic. > > Here's some code, > > final StreamJoined<String, TransactionEvent, BalanceEvent> joinParams = > StreamJoined.with( > STRING_SERDE, > StreamSerdeConstants.TRANSACTION_EVENT_SERDE, > StreamSerdeConstants.BALANCE_EVENT_SERDE); > > JoinWindows joinWindows = JoinWindows > .of(Duration.ofSeconds(streamsProperties.getJoinWindowDuration())) > .grace(Duration.ofSeconds(streamsProperties.getJoinGraceDuration())); > > ValueJoiner<TransactionEvent, BalanceEvent, BalanceHistoryEvent> > valueJoiner = > (transactionEvent, balanceEvent) -> buildMessage(balanceEvent, > transactionEvent); > > > transactions > // TODO: change to leftJoin > .join(beWithTransaction, valueJoiner, joinWindows, joinParams) > > > It's pretty simple, but for my use case I need to process in some way the > messages that are not joined, so I thought I could use a LEFT JOIN. But > according to my tests and this documentation > https://www.confluent.io/blog/crossing-streams-joins-apache-kafka/ > > I have seen in the end I could end up with both the combined message as the > regular inner join performs and the message with one side as NULL, for > example (A,B) and (A, null) > > I thought the JOIN Window could force the output of the left join to just > output if it found a match to just (A,B) not both. Maybe I have a bug in my > Window configuration > > Is there a way to force the behavior I need, meaning... using left join and > a JoinWindows output only one message (A,B) or (A, null) > > regards > - Miguel >
