Access elements of PCollectionView<List<Foo>> : Google Cloud Dataflow/Apache Beam

Question

I have a PCollection which I want to pass as a side-input and access its elements in a ParDo.

I've created a PCollectionView of it as:

final PCollectionView<List<Foo>> view =
    myPCollection.apply(View.asList());

How to access the elements of it in a ParDo when passed as a side-input?

An example would really help.

Thank You

Answer 1

This snippet mainly comes from the Beam programming guide.

final PCollectionView<List<Foo>> view =
               myPCollection.apply(View.asList());


PCollection<String> resultingPCollection =
someOtherPCollection.apply(ParDo
    .of(new DoFn<String, String>() {
        @ProcessElement
        public void processElement(ProcessContext c) {
          List<Foo> mySideInput = c.sideInput(view);
          // Do something with side input
        }
    }).withSideInputs(view)
);

If you don't want to use an anonymous DoFn, you can also pass the PCollectionView as part of its constructor and access it in the processElement function. Like so:

final PCollectionView<List<Foo>> view =
           myPCollection.apply(View.asList());


PCollection<String> resultingPCollection =
          someOtherPCollection.apply(ParDo
              .of(new MyDoFn(view)).withSideInputs(view));

class MyDoFn extends DoFn<String, String> {
  final PCollectionView<List<Foo>> view;

  MyDoFn(PCollectionView<List<Foo>> view) {
    this.view = view;
  }

  @ProcessElement
  public void processElement(ProcessContext c) {
    List<Foo> mySideInput = c.sideInput(this.view);
   // Do something with side input
  }
}