org.apache.kafka.streams.kstream

Interface KTable<K,V>

Type Parameters:

K - Type of primary keys

V - Type of value changes

@InterfaceStability.Unstable
public interface KTable<K,V>

KTable is an abstraction of a changelog stream from a primary-keyed table. Each record in this changelog stream is an update on the primary-keyed table with the record key as the primary key.

A KTable is either defined from a single Kafka topic that is consumed message by message or the result of a KTable transformation. An aggregation of a KStream also yields a KTable.

A KTable can be transformed record by record, joined with another KTable or KStream, or can be re-partitioned and aggregated into a new KTable.

Some KTables have an internal state (a ReadOnlyKeyValueStore) and are therefore queryable via the interactive queries API. For example:

final KTable table = ...
     ...
     final KafkaStreams streams = ...;
     streams.start()
     ...
     final String queryableStoreName = table.getStoreName(); // returns null if KTable is not queryable
     ReadOnlyKeyValueStore view = streams.store(queryableStoreName, QueryableStoreTypes.keyValueStore());
     view.get(key);

See Also:

KStream, KGroupedTable, GlobalKTable, KStreamBuilder.table(String, String)

Method Summary

Methods

Modifier and Type	Method and Description
KTable<K,V>	filter(Predicate<? super K,? super V> predicate) Create a new KTable that consists of all records of this KTable which satisfy the given predicate.
KTable<K,V>	filterNot(Predicate<? super K,? super V> predicate) Create a new KTable that consists all records of this KTable which do not satisfy the given predicate.
void	foreach(ForeachAction<? super K,? super V> action) Perform an action on each update record of this KTable.
String	getStoreName() Get the name of the local state store used for materializing this KTable.
<KR,VR> KGroupedTable<KR,VR>	groupBy(KeyValueMapper<? super K,? super V,KeyValue<KR,VR>> selector) Re-groups the records of this KTable using the provided KeyValueMapper and default serializers and deserializers.
<KR,VR> KGroupedTable<KR,VR>	groupBy(KeyValueMapper<? super K,? super V,KeyValue<KR,VR>> selector, Serde<KR> keySerde, Serde<VR> valueSerde) Re-groups the records of this KTable using the provided KeyValueMapper.
<VO,VR> KTable<K,VR>	join(KTable<K,VO> other, ValueJoiner<? super V,? super VO,? extends VR> joiner) Join records of this KTable with another KTable's records using non-windowed inner equi join.
<VO,VR> KTable<K,VR>	leftJoin(KTable<K,VO> other, ValueJoiner<? super V,? super VO,? extends VR> joiner) Join records of this KTable (left input) with another KTable's (right input) records using non-windowed left equi join.
<VR> KTable<K,VR>	mapValues(ValueMapper<? super V,? extends VR> mapper) Create a new KTable by transforming the value of each record in this KTable into a new value (with possible new type)in the new KTable.
<VO,VR> KTable<K,VR>	outerJoin(KTable<K,VO> other, ValueJoiner<? super V,? super VO,? extends VR> joiner) Join records of this KTable (left input) with another KTable's (right input) records using non-windowed outer equi join.
void	print() Print the update records of this KTable to System.out.
void	print(Serde<K> keySerde, Serde<V> valSerde) Print the update records of this KTable to System.out.
void	print(Serde<K> keySerde, Serde<V> valSerde, String streamName) Print the update records of this KTable to System.out.
void	print(String streamName) Print the update records of this KTable to System.out.
KTable<K,V>	through(Serde<K> keySerde, Serde<V> valSerde, StreamPartitioner<? super K,? super V> partitioner, String topic, String storeName) Materialize this changelog stream to a topic and creates a new KTable from the topic using a customizable StreamPartitioner to determine the distribution of records to partitions.
KTable<K,V>	through(Serde<K> keySerde, Serde<V> valSerde, String topic, String storeName) Materialize this changelog stream to a topic and creates a new KTable from the topic.
KTable<K,V>	through(StreamPartitioner<? super K,? super V> partitioner, String topic, String storeName) Materialize this changelog stream to a topic and creates a new KTable from the topic using default serializers and deserializers and a customizable StreamPartitioner to determine the distribution of records to partitions.
KTable<K,V>	through(String topic, String storeName) Materialize this changelog stream to a topic and creates a new KTable from the topic using default serializers and deserializers and producer's DefaultPartitioner.
void	to(Serde<K> keySerde, Serde<V> valSerde, StreamPartitioner<? super K,? super V> partitioner, String topic) Materialize this changelog stream to a topic using a customizable StreamPartitioner to determine the distribution of records to partitions.
void	to(Serde<K> keySerde, Serde<V> valSerde, String topic) Materialize this changelog stream to a topic.
void	to(StreamPartitioner<? super K,? super V> partitioner, String topic) Materialize this changelog stream to a topic using default serializers and deserializers and a customizable StreamPartitioner to determine the distribution of records to partitions.
void	to(String topic) Materialize this changelog stream to a topic using default serializers and deserializers and producer's DefaultPartitioner.
KStream<K,V>	toStream() Convert this changelog stream to a KStream.
<KR> KStream<KR,V>	toStream(KeyValueMapper<? super K,? super V,? extends KR> mapper) Convert this changelog stream to a KStream using the given KeyValueMapper to select the new key.
void	writeAsText(String filePath) Write the update records of this KTable to a file at the given path.
void	writeAsText(String filePath, Serde<K> keySerde, Serde<V> valSerde) Write the update records of this KTable to a file at the given path.
void	writeAsText(String filePath, String streamName) Write the update records of this KTable to a file at the given path.
void	writeAsText(String filePath, String streamName, Serde<K> keySerde, Serde<V> valSerde) Write the update records of this KTable to a file at the given path.

Method Detail

filter

KTable<K,V> filter(Predicate<? super K,? super V> predicate)

Create a new KTable that consists of all records of this KTable which satisfy the given predicate. All records that do not satisfy the predicate are dropped. For each KTable update the filter is evaluated on the update record to produce an update record for the result KTable. This is a stateless record-by-record operation.

Note that filter for a changelog stream works different to record stream filters, because records with null values (so-called tombstone records) have delete semantics. Thus, for tombstones the provided filter predicate is not evaluated but the tombstone record is forwarded directly if required (i.e., if there is anything to be deleted). Furthermore, for each record that gets dropped (i.e., dot not satisfied the given predicate) a tombstone record is forwarded.

Parameters:

predicate - a filter Predicate that is applied to each record

Returns:

a KTable that contains only those records that satisfy the given predicate

See Also:

filterNot(Predicate)

filterNot

KTable<K,V> filterNot(Predicate<? super K,? super V> predicate)

Create a new KTable that consists all records of this KTable which do not satisfy the given predicate. All records that do satisfy the predicate are dropped. For each KTable update the filter is evaluated on the update record to produce an update record for the result KTable. This is a stateless record-by-record operation.

Note that filterNot for a changelog stream works different to record stream filters, because records with null values (so-called tombstone records) have delete semantics. Thus, for tombstones the provided filter predicate is not evaluated but the tombstone record is forwarded directly if required (i.e., if there is anything to be deleted). Furthermore, for each record that gets dropped (i.e., does satisfy the given predicate) a tombstone record is forwarded.

Parameters:

predicate - a filter Predicate that is applied to each record

Returns:

a KTable that contains only those records that do not satisfy the given predicate

See Also:

filter(Predicate)

mapValues

<VR> KTable<K,VR> mapValues(ValueMapper<? super V,? extends VR> mapper)

Create a new KTable by transforming the value of each record in this KTable into a new value (with possible new type)in the new KTable. For each KTable update the provided ValueMapper is applied to the value of the update record and computes a new value for it, resulting in an update record for the result KTable. Thus, an input record <K,V> can be transformed into an output record <K:V'>. This is a stateless record-by-record operation.

The example below counts the number of token of the value string.

KTable<String, String> inputTable = builder.table("topic");
 KTable<String, Integer> outputTable = inputTable.mapValue(new ValueMapper<String, Integer> {
     Integer apply(String value) {
         return value.split(" ").length;
     }
 });
 

This operation preserves data co-location with respect to the key. Thus, no internal data redistribution is required if a key based operator (like a join) is applied to the result KTable.

Note that mapValues for a changelog stream works different to record stream filters, because records with null values (so-called tombstone records) have delete semantics. Thus, for tombstones the provided value-mapper is not evaluated but the tombstone record is forwarded directly to delete the corresponding record in the result KTable.

Type Parameters:

VR - the value type of the result KTable

Parameters:

mapper - a ValueMapper that computes a new output value

Returns:

a KTable that contains records with unmodified keys and new values (possibly of different type)

print

void print()

Print the update records of this KTable to System.out. This function will use the generated name of the parent processor node to label the key/value pairs printed to the console.

The provided serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that print() is not applied to the internal state store and only called for each new KTable update record.

print

void print(String streamName)

Print the update records of this KTable to System.out. This function will use the given name to label the key/value pairs printed to the console.

The provided serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that print() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

streamName - the name used to label the key/value pairs printed to the console

print

void print(Serde<K> keySerde,
         Serde<V> valSerde)

Print the update records of this KTable to System.out. This function will use the generated name of the parent processor node to label the key/value pairs printed to the console.

The provided serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that print() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

keySerde - key serde used to deserialize key if type is byte[],

valSerde - value serde used to deserialize value if type is byte[],

print

void print(Serde<K> keySerde,
         Serde<V> valSerde,
         String streamName)

Print the update records of this KTable to System.out. This function will use the given name to label the key/value pairs printed to the console.

The provided serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that print() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

keySerde - key serde used to deserialize key if type is byte[],

valSerde - value serde used to deserialize value if type is byte[],

streamName - the name used to label the key/value pairs printed to the console

writeAsText

void writeAsText(String filePath)

Write the update records of this KTable to a file at the given path. This function will use the generated name of the parent processor node to label the key/value pairs printed to the file.

The default serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that writeAsText() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

filePath - name of file to write to

writeAsText

void writeAsText(String filePath,
               String streamName)

Write the update records of this KTable to a file at the given path. This function will use the given name to label the key/value printed to the file.

The default serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that writeAsText() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

filePath - name of file to write to

streamName - the name used to label the key/value pairs printed out to the console

writeAsText

void writeAsText(String filePath,
               Serde<K> keySerde,
               Serde<V> valSerde)

Write the update records of this KTable to a file at the given path. This function will use the generated name of the parent processor node to label the key/value pairs printed to the file.

The provided serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that writeAsText() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

filePath - name of file to write to

keySerde - key serde used to deserialize key if type is byte[],

valSerde - value serde used to deserialize value if type is byte[],

writeAsText

void writeAsText(String filePath,
               String streamName,
               Serde<K> keySerde,
               Serde<V> valSerde)

Write the update records of this KTable to a file at the given path. This function will use the given name to label the key/value printed to the file.

The default serde will be used to deserialize the key or value in case the type is byte[] before calling toString() on the deserialized object.

Implementors will need to override toString() for keys and values that are not of type String, Integer etc. to get meaningful information.

Note that writeAsText() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

filePath - name of file to write to

streamName - the name used to label the key/value pairs printed to the console

keySerde - key serde used to deserialize key if type is byte[],

valSerde - value serde used to deserialize value if type is byte[],

foreach

void foreach(ForeachAction<? super K,? super V> action)

Perform an action on each update record of this KTable. Note that this is a terminal operation that returns void.

Note that foreach() is not applied to the internal state store and only called for each new KTable update record.

Parameters:

action - an action to perform on each record

toStream

KStream<K,V> toStream()

Convert this changelog stream to a KStream.

Note that this is a logical operation and only changes the "interpretation" of the stream, i.e., each record of this changelog stream is no longer treated as an update record (cf. KStream vs KTable).

Returns:

a KStream that contains the same records as this KTable

toStream

<KR> KStream<KR,V> toStream(KeyValueMapper<? super K,? super V,? extends KR> mapper)

Convert this changelog stream to a KStream using the given KeyValueMapper to select the new key.

For example, you can compute the new key as the length of the value string.

KTable<String, String> table = builder.table("topic");
 KTable<Integer, String> keyedStream = table.toStream(new KeyValueMapper<String, String, Integer> {
     Integer apply(String key, String value) {
         return value.length();
     }
 });
 

Setting a new key might result in an internal data redistribution if a key based operator (like an aggregation or join) is applied to the result KStream.

This operation is equivalent to calling table.toStream().selectKey(KeyValueMapper).

Note that toStream() is a logical operation and only changes the "interpretation" of the stream, i.e., each record of this changelog stream is no longer treated as an update record (cf. KStream vs KTable).

Type Parameters:

KR - the new key type of the result stream

Parameters:

mapper - a KeyValueMapper that computes a new key for each record

Returns:

a KStream that contains the same records as this KTable

through

KTable<K,V> through(String topic,
                  String storeName)

Materialize this changelog stream to a topic and creates a new KTable from the topic using default serializers and deserializers and producer's DefaultPartitioner. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

This is equivalent to calling #to(someTopicName) and KStreamBuilder#table(someTopicName, queryableStoreName).

The resulting KTable will be materialized in a local state store with the given store name (cf. KStreamBuilder.table(String, String))

Parameters:

topic - the topic name

storeName - the state store name used for the result KTable

Returns:

a KTable that contains the exact same (and potentially repartitioned) records as this KTable

through

KTable<K,V> through(StreamPartitioner<? super K,? super V> partitioner,
                  String topic,
                  String storeName)

Materialize this changelog stream to a topic and creates a new KTable from the topic using default serializers and deserializers and a customizable StreamPartitioner to determine the distribution of records to partitions. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

This is equivalent to calling #to(partitioner, someTopicName) and KStreamBuilder#table(someTopicName, queryableStoreName).

The resulting KTable will be materialized in a local state store with the given store name (cf. KStreamBuilder.table(String, String))

Parameters:

partitioner - the function used to determine how records are distributed among partitions of the topic, if not specified producer's DefaultPartitioner will be used

topic - the topic name

storeName - the state store name used for the result KTable

Returns:

a KTable that contains the exact same (and potentially repartitioned) records as this KTable

through

KTable<K,V> through(Serde<K> keySerde,
                  Serde<V> valSerde,
                  String topic,
                  String storeName)

Materialize this changelog stream to a topic and creates a new KTable from the topic. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

If keySerde provides a WindowedSerializer for the key WindowedStreamPartitioner is used—otherwise producer's DefaultPartitioner is used.

This is equivalent to calling #to(keySerde, valueSerde, someTopicName) and KStreamBuilder#table(someTopicName, queryableStoreName).

The resulting KTable will be materialized in a local state store with the given store name (cf. KStreamBuilder.table(String, String))

Parameters:

keySerde - key serde used to send key-value pairs, if not specified the default key serde defined in the configuration will be used

valSerde - value serde used to send key-value pairs, if not specified the default value serde defined in the configuration will be used

topic - the topic name

storeName - the state store name used for the result KTable

Returns:

a KTable that contains the exact same (and potentially repartitioned) records as this KTable

through

KTable<K,V> through(Serde<K> keySerde,
                  Serde<V> valSerde,
                  StreamPartitioner<? super K,? super V> partitioner,
                  String topic,
                  String storeName)

Materialize this changelog stream to a topic and creates a new KTable from the topic using a customizable StreamPartitioner to determine the distribution of records to partitions. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

This is equivalent to calling #to(keySerde, valueSerde, partitioner, someTopicName) and KStreamBuilder#table(someTopicName, queryableStoreName).

The resulting KTable will be materialized in a local state store with the given store name (cf. KStreamBuilder.table(String, String))

Parameters:

keySerde - key serde used to send key-value pairs, if not specified the default key serde defined in the configuration will be used

valSerde - value serde used to send key-value pairs, if not specified the default value serde defined in the configuration will be used

partitioner - the function used to determine how records are distributed among partitions of the topic, if not specified and keySerde provides a WindowedSerializer for the key WindowedStreamPartitioner will be used—otherwise DefaultPartitioner will be used

topic - the topic name

storeName - the state store name used for the result KTable

Returns:

a KTable that contains the exact same (and potentially repartitioned) records as this KTable

to

void to(String topic)

Materialize this changelog stream to a topic using default serializers and deserializers and producer's DefaultPartitioner. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

Parameters:

topic - the topic name

to

void to(StreamPartitioner<? super K,? super V> partitioner,
      String topic)

Materialize this changelog stream to a topic using default serializers and deserializers and a customizable StreamPartitioner to determine the distribution of records to partitions. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

Parameters:

partitioner - the function used to determine how records are distributed among partitions of the topic, if not specified producer's DefaultPartitioner will be used

topic - the topic name

to

void to(Serde<K> keySerde,
      Serde<V> valSerde,
      String topic)

Materialize this changelog stream to a topic. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

If keySerde provides a WindowedSerializer for the key WindowedStreamPartitioner is used—otherwise producer's DefaultPartitioner is used.

Parameters:

keySerde - key serde used to send key-value pairs, if not specified the default key serde defined in the configuration will be used

valSerde - value serde used to send key-value pairs, if not specified the default value serde defined in the configuration will be used

topic - the topic name

to

void to(Serde<K> keySerde,
      Serde<V> valSerde,
      StreamPartitioner<? super K,? super V> partitioner,
      String topic)

Materialize this changelog stream to a topic using a customizable StreamPartitioner to determine the distribution of records to partitions. The specified topic should be manually created before it is used (i.e., before the Kafka Streams application is started).

Parameters:

keySerde - key serde used to send key-value pairs, if not specified the default key serde defined in the configuration will be used

valSerde - value serde used to send key-value pairs, if not specified the default value serde defined in the configuration will be used

partitioner - the function used to determine how records are distributed among partitions of the topic, if not specified and keySerde provides a WindowedSerializer for the key WindowedStreamPartitioner will be used—otherwise DefaultPartitioner will be used

topic - the topic name

groupBy

<KR,VR> KGroupedTable<KR,VR> groupBy(KeyValueMapper<? super K,? super V,KeyValue<KR,VR>> selector)

Re-groups the records of this KTable using the provided KeyValueMapper and default serializers and deserializers. Each KeyValue pair of this KTable is mapped to a new KeyValue pair by applying the provided KeyValueMapper. Re-grouping a KTable is required before an aggregation operator can be applied to the data (cf. KGroupedTable). The KeyValueMapper selects a new key and value (with should both have unmodified type). If the new record key is null the record will not be included in the resulting KGroupedTable

Because a new key is selected, an internal repartitioning topic will be created in Kafka. This topic will be named "${applicationId}-XXX-repartition", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "XXX" is an internally generated name, and "-repartition" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

All data of this KTable will be redistributed through the repartitioning topic by writing all update records to and rereading all update records from it, such that the resulting KGroupedTable is partitioned on the new key.

If the key or value type is changed, it is recommended to use groupBy(KeyValueMapper, Serde, Serde) instead.

Type Parameters:

KR - the key type of the result KGroupedTable

VR - the value type of the result KGroupedTable

Parameters:

selector - a KeyValueMapper that computes a new grouping key and value to be aggregated

Returns:

a KGroupedTable that contains the re-grouped records of the original KTable

groupBy

<KR,VR> KGroupedTable<KR,VR> groupBy(KeyValueMapper<? super K,? super V,KeyValue<KR,VR>> selector,
                                   Serde<KR> keySerde,
                                   Serde<VR> valueSerde)

Re-groups the records of this KTable using the provided KeyValueMapper. Each KeyValue pair of this KTable is mapped to a new KeyValue pair by applying the provided KeyValueMapper. Re-grouping a KTable is required before an aggregation operator can be applied to the data (cf. KGroupedTable). The KeyValueMapper selects a new key and value (both with potentially different type). If the new record key is null the record will not be included in the resulting KGroupedTable

Because a new key is selected, an internal repartitioning topic will be created in Kafka. This topic will be named "${applicationId}-XXX-repartition", where "applicationId" is user-specified in StreamsConfig via parameter APPLICATION_ID_CONFIG, "XXX" is an internally generated name, and "-repartition" is a fixed suffix. You can retrieve all generated internal topic names via KafkaStreams.toString().

All data of this KTable will be redistributed through the repartitioning topic by writing all update records to and rereading all update records from it, such that the resulting KGroupedTable is partitioned on the new key.

Type Parameters:

KR - the key type of the result KGroupedTable

VR - the value type of the result KGroupedTable

Parameters:

selector - a KeyValueMapper that computes a new grouping key and value to be aggregated

keySerde - key serdes for materializing this stream, if not specified the default serdes defined in the configs will be used

valueSerde - value serdes for materializing this stream, if not specified the default serdes defined in the configs will be used

Returns:

a KGroupedTable that contains the re-grouped records of the original KTable

join

<VO,VR> KTable<K,VR> join(KTable<K,VO> other,
                        ValueJoiner<? super V,? super VO,? extends VR> joiner)

Join records of this KTable with another KTable's records using non-windowed inner equi join. The join is a primary key join with join attribute thisKTable.key == otherKTable.key. The result is an ever updating KTable that represents the current (i.e., processing time) result of the join.

The join is computed by (1) updating the internal state of one KTable and (2) performing a lookup for a matching record in the current (i.e., processing time) internal state of the other KTable. This happens in a symmetric way, i.e., for each update of either this or the other input KTable the result gets updated.

For each KTable record that finds a corresponding record in the other KTable the provided ValueJoiner will be called to compute a value (with arbitrary type) for the result record. The key of the result record is the same as for both joining input records.

Note that records with null values (so-called tombstone records) have delete semantics. Thus, for input tombstones the provided value-joiner is not called but a tombstone record is forwarded directly to delete a record in the result KTable if required (i.e., if there is anything to be deleted).

Input records with null key will be dropped and no join computation is performed.

Example:

thisKTable	thisState	otherKTable	otherState	result update record
<K1:A>	<K1:A>
	<K1:A>	<K1:b>	<K1:b>	<K1:ValueJoiner(A,b)>
<K1:C>	<K1:C>		<K1:b>	<K1:ValueJoiner(C,b)>
	<K1:C>	<K1:null>		<K1:null>

Both input streams (or to be more precise, their underlying source topics) need to have the same number of partitions.

Type Parameters:

VO - the value type of the other KTable

VR - the value type of the result KTable

Parameters:

other - the other KTable to be joined with this KTable

joiner - a ValueJoiner that computes the join result for a pair of matching records

Returns:

a KTable that contains join-records for each key and values computed by the given ValueJoiner, one for each matched record-pair with the same key

See Also:

leftJoin(KTable, ValueJoiner), outerJoin(KTable, ValueJoiner)

leftJoin

<VO,VR> KTable<K,VR> leftJoin(KTable<K,VO> other,
                            ValueJoiner<? super V,? super VO,? extends VR> joiner)

Join records of this KTable (left input) with another KTable's (right input) records using non-windowed left equi join. The join is a primary key join with join attribute thisKTable.key == otherKTable.key. In contrast to inner-join, all records from left KTable will produce an output record (cf. below). The result is an ever updating KTable that represents the current (i.e., processing time) result of the join.

The join is computed by (1) updating the internal state of one KTable and (2) performing a lookup for a matching record in the current (i.e., processing time) internal state of the other KTable. This happens in a symmetric way, i.e., for each update of either this or the other input KTable the result gets updated.

For each KTable record that finds a corresponding record in the other KTable's state the provided ValueJoiner will be called to compute a value (with arbitrary type) for the result record. Additionally, for each record of left KTable that does not find a corresponding record in the right KTable's state the provided ValueJoiner will be called with rightValue = null to compute a value (with arbitrary type) for the result record. The key of the result record is the same as for both joining input records.

Note that records with null values (so-called tombstone records) have delete semantics. For example, for left input tombstones the provided value-joiner is not called but a tombstone record is forwarded directly to delete a record in the result KTable if required (i.e., if there is anything to be deleted).

Input records with null key will be dropped and no join computation is performed.

Example:

thisKTable	thisState	otherKTable	otherState	result update record
<K1:A>	<K1:A>			<K1:ValueJoiner(A,null)>
	<K1:A>	<K1:b>	<K1:b>	<K1:ValueJoiner(A,b)>
<K1:null>			<K1:b>	<K1:null>
		<K1:null>

Both input streams (or to be more precise, their underlying source topics) need to have the same number of partitions.

Type Parameters:

VO - the value type of the other KTable

VR - the value type of the result KTable

Parameters:

other - the other KTable to be joined with this KTable

joiner - a ValueJoiner that computes the join result for a pair of matching records

Returns:

a KTable that contains join-records for each key and values computed by the given ValueJoiner, one for each matched record-pair with the same key plus one for each non-matching record of left KTable

See Also:

join(KTable, ValueJoiner), outerJoin(KTable, ValueJoiner)

outerJoin

<VO,VR> KTable<K,VR> outerJoin(KTable<K,VO> other,
                             ValueJoiner<? super V,? super VO,? extends VR> joiner)

Join records of this KTable (left input) with another KTable's (right input) records using non-windowed outer equi join. The join is a primary key join with join attribute thisKTable.key == otherKTable.key. In contrast to inner-join or left-join, all records from both input KTables will produce an output record (cf. below). The result is an ever updating KTable that represents the current (i.e., processing time) result of the join.

The join is computed by (1) updating the internal state of one KTable and (2) performing a lookup for a matching record in the current (i.e., processing time) internal state of the other KTable. This happens in a symmetric way, i.e., for each update of either this or the other input KTable the result gets updated.

For each KTable record that finds a corresponding record in the other KTable's state the provided ValueJoiner will be called to compute a value (with arbitrary type) for the result record. Additionally, for each record that does not find a corresponding record in the corresponding other KTable's state the provided ValueJoiner will be called with null value for the corresponding other value to compute a value (with arbitrary type) for the result record. The key of the result record is the same as for both joining input records.

Note that records with null values (so-called tombstone records) have delete semantics. Thus, for input tombstones the provided value-joiner is not called but a tombstone record is forwarded directly to delete a record in the result KTable if required (i.e., if there is anything to be deleted).

Input records with null key will be dropped and no join computation is performed.

Example:

thisKTable	thisState	otherKTable	otherState	result update record
<K1:A>	<K1:A>			<K1:ValueJoiner(A,null)>
	<K1:A>	<K1:b>	<K1:b>	<K1:ValueJoiner(A,b)>
<K1:null>			<K1:b>	<K1:ValueJoiner(null,b)>
		<K1:null>		<K1:null>

Both input streams (or to be more precise, their underlying source topics) need to have the same number of partitions.

Type Parameters:

VO - the value type of the other KTable

VR - the value type of the result KTable

Parameters:

other - the other KTable to be joined with this KTable

joiner - a ValueJoiner that computes the join result for a pair of matching records

Returns:

a KTable that contains join-records for each key and values computed by the given ValueJoiner, one for each matched record-pair with the same key plus one for each non-matching record of both KTables

See Also:

join(KTable, ValueJoiner), leftJoin(KTable, ValueJoiner)

getStoreName

String getStoreName()

Get the name of the local state store used for materializing this KTable.

Returns:

the underlying state store name, or null if this KTable is not materialized