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https://issues.apache.org/jira/browse/BEAM-247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15267496#comment-15267496
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Pei He commented on BEAM-247:
-----------------------------
The bug report comes from the following code snippets, and the combine fn is
not used in a correct way:
"""
when I do this:
PCollection<KV<String, Double>> salesRecords = p.apply(Create.of(KV.of("a",
1.0), KV.of("b", 2.0)));
PCollection<KV<String, Double>> totalSalesPerPerson =
salesRecords.apply(Combine.<String, Double>perKey(
new Sum.SumDoubleFn()));
I get this error (and only this error):
[ERROR]
/Users/stephen/dev/dominion/AnalyzeGames/src/main/java/com/siskybiz/dominion/StarterPipeline.java:[138,10]
incompatible types: com.google.cloud.dataflow.sdk.transforms.Sum.SumDoubleFn
cannot be converted to
com.google.cloud.dataflow.sdk.transforms.SerializableFunction<java.lang.Iterable<java.lang.Double>,java.lang.Double>
"""
The correct usage is:
salesRecords.apply(Combine.<String, Double, Double>perKey(new
Sum.SumDoubleFn()));
or
salesRecords.apply(Combine.perKey(new
Sum.SumDoubleFn().<String>asKeyedFn()));
> CombineFn's only definable/usable inside sdk.transforms package
> ---------------------------------------------------------------
>
> Key: BEAM-247
> URL: https://issues.apache.org/jira/browse/BEAM-247
> Project: Beam
> Issue Type: Bug
> Components: sdk-java-core
> Reporter: Ben Chambers
> Assignee: Pei He
> Priority: Critical
>
> {code:java}
> public abstract static class CombineFn<InputT, AccumT, OutputT>
> extends AbstractGlobalCombineFn<InputT, AccumT, OutputT> { /* ... */ }
> abstract static class AbstractGlobalCombineFn<InputT, AccumT, OutputT>
> implements GlobalCombineFn<InputT, AccumT, OutputT>, Serializable { /* ...
> */ }
> {code}
> Since {{AbstractGlobalCombineFn}} is package protected (and therefore not
> visible outside of the {{transform}} package, it is not possible to cast any
> class that extends {{CombineFn}} to a {{GlobalCombineFn}} outside of this
> package.
> This prevents applying existing {{CombineFns}} directly (such as
> {{Combine.perKey(new Sum.SumIntegersFn())}}, as used in our documentation)
> and also means that a user cannot define their own {{CombineFn}} unless they
> put them in the {{transform}} package.
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