KStream ve KTable Duality

Giriş

Açıklaması şöyle

The duality between KStream and KTable lies in the fact that you can convert between these two representations, allowing you to switch between stream-like and table-like processing as needed:

KStream to KTable: You can convert a KStream into a KTable using operations like groupByKey followed by aggregation. This is useful when you want to create a table from a stream, aggregating data over a period of time.

KTable to KStream: Conversely, you can convert a KTable into a KStream. This allows you to turn a table-like representation into a stream for further processing or for joining with other streams.

Şeklen şöyle

KStream to KTable

groupBy metodu ile bir KGroupedStream elde edilir. İmzası şöyle

<KR> KGroupedStream<KR,V> groupBy(KeyValueMapper<? super K,? super V,KR> keySelector)
<KR> KGroupedStream<KR,V> groupBy(KeyValueMapper<? super K,? super V,KR> keySelector,
  Grouped<KR,V> grouped)
KGroupedStream<K,V>	groupByKey()
KGroupedStream<K,V>	groupByKey(Grouped<K,V> grouped)

KGroupedStream ise KTable'a dönüş sağlayan aggregate, count, reduce gibi sağlıyor. Örneğin count metodunun imzası şöyle

KTable<K,Long> count()