The type inference doesn't currently work for the join functions in Scala as it doesn't know yet the types of the given KStream[K, V] or KTable[K, V].
The fix here is to curry the joiner function. I personally prefer this notation but this also means it differs more from the Java API.
I believe the diff with the Java API is worth in this case as it's not only solving the type inference but also fits better the Scala way of coding (ex: fold).
Moreover any Scala dev will bug and spend little time on these functions trying to understand why the type inference is not working and then get frustrated to be obliged to be explicit here where it's not harmful to be inferred.
Reviewers: Debasish Ghosh <dghosh@acm.org>, Guozhang Wang <guozhang@confluent.io>, Ismael Juma <ismael@juma.me.uk>
Serdes are confusing in the Scala wrapper:
* We have wrappers around Serializer, Deserializer and Serde which are not very useful.
* We have Serdes in 2 places org.apache.kafka.common.serialization.Serde and in DefaultSerdes, instead we should be having only one place where to find all the Serdes.
I wanted to do this PR before the release as this is a breaking change.
This shouldn't add more so the current tests should be enough.
Reviewers: Debasish Ghosh <dghosh@acm.org>, Guozhang Wang <guozhang@confluent.io>
Reviewer: Matthias J. Sax <matthias@confluent.io>, Debasish Ghosh <dghosh@acm.org>, Guozhang Wang <guozhang@confluent.io>, Bill Bejeck <bill@confluent.io>
Several build and documentation updates were required after the merge of KAFKA-6670: Implement a Scala wrapper library for Kafka Streams.
Encode Scala major version into streams-scala artifacts.
To differentiate versions of the kafka-streams-scala artifact across Scala major versions it's required to encode the version into the artifact name before its published to a maven repository. This is accomplished by following a similar release process as kafka core, which encodes the Scala major version and then runs the build for each major version of Scala supported. This is considered standard practice when releasing Scala libraries, but is not handled for us automatically with the basic Scala for Gradle support.
After this change you can generate and install the kafka-streams-scala artifact into the local maven repository:
$ ./gradlew -PscalaVersion=2.11 install
$ ./gradlew -PscalaVersion=2.12 install
Reviewers: Ismael Juma <ismael@juma.me.uk>, Guozhang Wang <wangguoz@gmail.com>
While working on this, I also refactored the MockProcessor out of the MockProcessorSupplier to cleanup the unit test paths.
Reviewers: John Roesler <john@confluent.io>, Bill Bejeck <bill@confluent.io>, Matthias J. Sax <matthias@confluent.io>
This PR implements a Scala wrapper library for Kafka Streams. The library is implemented as a project under streams, namely `:streams:streams-scala`. The PR contains the following:
* the library implementation of the wrapper abstractions
* the test suite
* the changes in `build.gradle` to build the library jar
The library has been tested running the tests as follows:
```
$ ./gradlew -Dtest.single=StreamToTableJoinScalaIntegrationTestImplicitSerdes streams:streams-scala:test
$ ./gradlew -Dtest.single=StreamToTableJoinScalaIntegrationTestImplicitSerdesWithAvro streams:streams-scala:test
$ ./gradlew -Dtest.single=WordCountTest streams:streams-scala:test
```
Author: Debasish Ghosh <ghosh.debasish@gmail.com>
Author: Sean Glover <seglo@randonom.com>
Reviewers: Bill Bejeck <bill@confluent.io>, Matthias J. Sax <matthias@confluent.io>, Ismael Juma <ismael@juma.me.uk>, John Roesler <john@confluent.io>, Damian Guy <damian@confluent.io>, Guozhang Wang <wangguoz@gmail.com>
Closes#4756 from debasishg/scala-streams
Joan Goyeau
Andy Coates
Guozhang Wang
Michael G. Noll
Sean Glover
Debasish Ghosh