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https://issues.apache.org/jira/browse/KAFKA-3745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15297299#comment-15297299
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Guozhang Wang commented on KAFKA-3745:
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I may be still getting your motivations wrong, so just for clarification: for
{{ValueJoiner}} interface it has
{code}
R apply(V1 value1, V2 value2);
{code}
And hence the key is not provided in the function, since we thought for common
cases it is not needed for the join computation itself. Are you suggesting to
add this key as:
{code}
R apply(K key, V1 value1, V2 value2);
{code}
for your specific scenario? From the description above I am not sure if that is
the case.
> Consider adding join key to ValueJoiner interface
> -------------------------------------------------
>
> Key: KAFKA-3745
> URL: https://issues.apache.org/jira/browse/KAFKA-3745
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 0.10.0.0
> Reporter: Greg Fodor
> Priority: Minor
> Labels: api, newbie
>
> In working with Kafka Stream joining, it's sometimes the case that a join key
> is not actually present in the values of the joins themselves (if, for
> example, a previous transform generated an ephemeral join key.) In such
> cases, the actual key of the join is not available in the ValueJoiner
> implementation to be used to construct the final joined value. This can be
> worked around by explicitly threading the join key into the value if needed,
> but it seems like extending the interface to pass the join key along as well
> would be helpful.
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