[GitHub] [kafka] JoelWee commented on a change in pull request #9186: KAFKA-10277: Allow null keys with non-null mappedKey in KStreamKGlobalTable join

[GitBox <gi...@apache.org>]

JoelWee commented on a change in pull request #9186:
URL: https://github.com/apache/kafka/pull/9186#discussion_r475196944



##########
File path: streams/src/main/java/org/apache/kafka/streams/kstream/internals/KStreamKTableJoinProcessor.java
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@@ -58,29 +60,46 @@ public void init(final ProcessorContext context) {
 
     @Override
     public void process(final K1 key, final V1 value) {
-        // we do join iff keys are equal, thus, if key is null we cannot join and just ignore the record
-        // If {@code keyMapper} returns {@code null} it implies there is no match,
-        // so ignore unless it is a left join
+        // we do join iff the joining keys are equal, thus, if the mappedKey is null we cannot join
+        // and just ignore the record.
         //
         // we also ignore the record if value is null, because in a key-value data model a null-value indicates
         // an empty message (ie, there is nothing to be joined) -- this contrast SQL NULL semantics
         // furthermore, on left/outer joins 'null' in ValueJoiner#apply() indicates a missing record --
         // thus, to be consistent and to avoid ambiguous null semantics, null values are ignored
-        if (key == null || value == null) {
+        final Optional<K2> maybeMappedKey = maybeExtractMappedKey(key, value);
+        if (!maybeMappedKey.isPresent()) {
             LOG.warn(
                 "Skipping record due to null key or value. key=[{}] value=[{}] topic=[{}] partition=[{}] offset=[{}]",
                 key, value, context().topic(), context().partition(), context().offset()
             );
             droppedRecordsSensor.record();
         } else {
-            final K2 mappedKey = keyMapper.apply(key, value);
-            final V2 value2 = mappedKey == null ? null : getValueOrNull(valueGetter.get(mappedKey));

Review comment:
       `maybeExtractMappedKey` will return `Optional.empty()` if the `mappedKey` is null. So `mappedKey` will never be null in this portion of the code and we can skip the check I think




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