apache-kafka - Kafka Stream 在 KTable 值字段上分组

Question

我有一个用例，我的 KTable 是这样的。

KTable : 订单表

键:值

{123} : {id1,12}

{124} : {id2,10}

{125} : {id1,5}

{126} : {id2,11}

KTable : orderByIdTable => 这个表会在 groupBy Value field (id) 和 count 列值的总和为 id1=(12+5) , id2=(10+11)

键:值

{id1} : {17}

{id2} : {21}

         final KTable<String, Order> orderTable = builder.table("order-topic");
         Don't know how to do this further.....
         final KTable<String,Long> orderByIdTable = ?

Answer 1

这是一个代码示例(仅使用 Java 基本类型，这使我可以更快地组合在一起)演示如何重新键控也就是重新分区 KTable，从而产生新的 KTable。您应该能够轻松地使其适应您转动 KTable<String, Order> 的示例进入KTable<String, Long> .

就我个人而言，我会为您的用例选择变体 2。

示例如下。 未完全测试，可能是墓碑记录(具有非空键但空值的消息，表示应从表中删除该键)未正确处理。

final StreamsBuilder builder = new StreamsBuilder();
final KTable<Integer, String> table = builder.table(inputTopic, Consumed.with(Serdes.Integer(), Serdes.String()));

// Variant 1 (https://docs.confluent.io/current/streams/faq.html#option-1-write-kstream-to-ak-read-back-as-ktable)
// Here, we re-key the KTable, write the results to a new topic, and then re-read that topic into a new KTable.
table
    .toStream()
    .map((key, value) -> KeyValue.pair(value, key))
    .to(outputTopic1, Produced.with(Serdes.String(), Serdes.Integer()));
KTable<String, Integer> rekeyedTable1 =
    builder.table(outputTopic1, Consumed.with(Serdes.String(), Serdes.Integer()));

// Variant 2 (https://docs.confluent.io/current/streams/faq.html#option-2-perform-a-dummy-aggregation)
// Here, we re-key the KTable (resulting in a KGroupedTable), and then perform a dummy aggregation to turn the
// KGroupedTable into a KTable.
final KTable<String, Integer> rekeyedTable2 =
    table
        .groupBy(
            (key, value) -> KeyValue.pair(value, key),
            Grouped.with(Serdes.String(), Serdes.Integer())
        )
        // Dummy aggregation
        .reduce(
            (aggValue, newValue) -> newValue, /* adder */
            (aggValue, oldValue) -> oldValue  /* subtractor */
        );
rekeyedTable2.toStream().to(outputTopic2, Produced.with(Serdes.String(), Serdes.Integer()));