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https://issues.apache.org/jira/browse/STREAMPIPES-449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17433430#comment-17433430
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Dominik Riemer commented on STREAMPIPES-449:
--------------------------------------------
This code is in the Compose pipeline element, which merges two input data
streams. Users can select fields from each of two input data streams, which are
merged into a single output event.
In the UI, users can select the fields.
Let's say, we have one input data stream \{"timestamp": 1234, "count": 12} and
another input stream like \{"timestamp": 2323, "temperature": 12} and you would
like to produce an output stream with the schema \{timestamp, count,
temperature}.
To distinguish between the fields from each input data stream, which might have
the same runtime name (see timestamp), a sleector prefix is internally added to
the event. So internally, timestamp from stream one is represented with the
prefix s0 (s0::timestamp) and from the second stream as (s1::timestamp).
The selector is automatically added based on user input in the UI. The
getSubset method is just a helper method to extract all matching fields based
on selected user input.
To get a better understanding, it probably helps to first start with a pipeline
element that only requires a single input stream and then move on to elements
that rely on two input streams.
E.g., have a look at the NumericalFilter or TextFilter components.
> Update Processing Element API in module streampipes-processors-filters-jvm
> --------------------------------------------------------------------------
>
> Key: STREAMPIPES-449
> URL: https://issues.apache.org/jira/browse/STREAMPIPES-449
> Project: StreamPipes
> Issue Type: Improvement
> Components: Pipeline Elements
> Reporter: Philipp Zehnder
> Priority: Major
> Fix For: 0.69.0
>
>
> The processors in this module use the old API, where 3 classes are required
> for a single processing element.
> These should be updated to use StreamPipesDataProcessor instead of
> StreamPipesDataProcessor.
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