Till Rohrmann created FLINK-3538:
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Summary: DataStream join API does not enforce consistent usage
Key: FLINK-3538
URL: https://issues.apache.org/jira/browse/FLINK-3538
Project: Flink
Issue Type: Improvement
Components: DataStream API, Scala API
Affects Versions: 1.0.0
Reporter: Till Rohrmann
In the Scala DataStream API the {{join}} operation does not enforce that the
user has specified a {{KeySelector}} for both input sides before applying a
window function. Moreover, the order of the {{where}} and {{equalTo}} clause is
not fixed and it is possible to specify multiple {{where}} and {{equalTo}}
clauses. In the latter case, it is not clear which {{KeySelector}} will
eventually be used by the system.
So the following Flink programs compile without a compilation problem (the
first two lines will only fail at runtime):
{code}
inputA.join(inputB).equalTo{x =>
x}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
.apply(new DefaultFlatJoinFunction[String, String]()).print()
inputA.join(inputB).where{x =>
x}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
.apply(new DefaultFlatJoinFunction[String, String]()).print()
inputA.join(inputB).equalTo{x => x}.where{x => x}.where{x => "1"}.equalTo{x =>
"42"}.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
.apply(new DefaultFlatJoinFunction[String, String]()).print()
{code}
This is unlike the Java DataStream API where a clear pattern of {{join}} then
{{where}} and then {{equalTo}} is enforced. I would propose to do the same for
the Scala API.
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