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From Cemalettin Koç (JIRA) <j...@apache.org>
Subject [jira] [Commented] (KAFKA-6713) Provide an easy way replace store with a custom one on High-Level Streams DSL
Date Mon, 26 Mar 2018 20:27:00 GMT

    [ https://issues.apache.org/jira/browse/KAFKA-6713?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16414477#comment-16414477

Cemalettin Koç commented on KAFKA-6713:

Today I came across another scenario which is still not very clear for me. :) For my use
case I have chosen our "Category" entity since It is updated rarely and it is data cardinality
is suitable for a newbie Kafka user. :) 

GlobalKTable is very nice since it is magically filling our in memory stores. However there
are some cases I need to invalidate some computed data which is based whole data of store. 

Please forgive my ignorance since I have just started to use Kafka but I thought It would
be nice to have something like KStream as GlobalKStream. :) I can process and trigger some
invalidation in case a new updated category? 

> Provide an easy way replace store with a custom one on High-Level Streams DSL
> -----------------------------------------------------------------------------
>                 Key: KAFKA-6713
>                 URL: https://issues.apache.org/jira/browse/KAFKA-6713
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>    Affects Versions: 1.0.1
>            Reporter: Cemalettin Koç
>            Priority: Major
>              Labels: streaming-api
>         Attachments: BytesTypeConverter.java, DelegatingByteStore.java, TypeConverter.java
> I am trying to use GlobalKTable with a custom store implementation. In my stores, I would
like to store my `Category` entites and I would like to query them by their name as well.
My custom store has some capabilities beyond `get` such as get by `name`. I also want to get
all entries in a hierarchical way in a lazy fashion. I have other use cases as well.
> In order to accomplish my task I had to implement  a custom `KeyValueBytesStoreSupplier`, 
`BytesTypeConverter` and 
> {code:java}
> public class DelegatingByteStore<K, V> implements KeyValueStore<Bytes, byte[]>
>   private BytesTypeConverter<K, V> converter;
>   private KeyValueStore<K, V> delegated;
>   public DelegatingByteStore(KeyValueStore<K, V> delegated, BytesTypeConverter<K,
V> converter) {
>     this.converter = converter;
>     this.delegated = delegated;
>   }
>   @Override
>   public void put(Bytes key, byte[] value) {
>     delegated.put(converter.outerKey(key),
>                   converter.outerValue(value));
>   }
>   @Override
>   public byte[] putIfAbsent(Bytes key, byte[] value) {
>     V v = delegated.putIfAbsent(converter.outerKey(key),
>                                 converter.outerValue(value));
>     return v == null ? null : value;
>   }
>   ......
> {code}
>  Type Converter:
> {code:java}
> public interface TypeConverter<K, IK, V, IV> {
>   IK innerKey(final K key);
>   IV innerValue(final V value);
>   List<KeyValue<IK, IV>> innerEntries(final List<KeyValue<K, V>>
>   List<KeyValue<K, V>> outerEntries(final List<KeyValue<Bytes, byte[]>>
>   V outerValue(final IV value);
>   KeyValue<K, V> outerKeyValue(final KeyValue<IK, IV> from);
>   KeyValue<Bytes, byte[]>innerKeyValue(final KeyValue<K, V> entry);
>   K outerKey(final IK ik);
> }
> {code}
> This is unfortunately too cumbersome and hard to maintain.  

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