mjsax commented on a change in pull request #9186:
URL: https://github.com/apache/kafka/pull/9186#discussion_r485096090
##########
File path:
streams/src/main/java/org/apache/kafka/streams/kstream/internals/KStreamKTableJoinProcessor.java
##########
@@ -58,22 +58,23 @@ 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,
+ // We allow null keys unless {@code keyMapper} returns {@code null}
and we ignore it as invalid.
+ // This happens for GlobalKTables but never for KTables since
keyMapper just returns the key.
+ // For non-null keys, if {@code keyMapper} returns {@code null} it
implies there is no match,
// so ignore unless it is a left join
//
// 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 K2 mappedKey = keyMapper.apply(key, value);
+ if ((key == null && mappedKey == null) || (!leftJoin && mappedKey ==
null) || value == null) {
Review comment:
This condition seems unnecessary complex. Should it not just be:
```
if (mappedKey == null || value == null) {
```
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