sdks/java/extensions/join-library/README.md

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Join-library
============

Join-library provides inner join, outer left and right join functions to
Apache Beam. The aim is to simplify the most common cases of join to a
simple function call.

The functions are generic so it supports join of any types supported by
Beam. Input to the join functions are PCollections of Key/Values. Both the
left and right PCollections need the same type for the key. All the join
functions return a Key/Value where Key is the join key and value is
a Key/Value where the key is the left value and right is the value.

In the cases of outer join, since null cannot be serialized the user have
to provide a value that represent null for that particular use case.

Example how to use join-library:

    PCollection<KV<String, String>> leftPcollection = ...
    PCollection<KV<String, Long>> rightPcollection = ...

    PCollection<KV<String, KV<String, Long>>> joinedPcollection =
      Join.innerJoin(leftPcollection, rightPcollection);