runners/samza/src/main/java/org/apache/beam/runners/samza/translation/SamzaPublishViewTransformOverride.java

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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.beam.runners.samza.translation;

import org.apache.beam.runners.core.Concatenate;
import org.apache.beam.runners.core.construction.SingleInputOutputOverrideFactory;
import org.apache.beam.sdk.runners.AppliedPTransform;
import org.apache.beam.sdk.transforms.Combine;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.View;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionView;
import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Iterables;

/** Samza override for {@link View} (side input) transforms. */
class SamzaPublishViewTransformOverride<ElemT, ViewT>
    extends SingleInputOutputOverrideFactory<
        PCollection<ElemT>, PCollection<ElemT>, View.CreatePCollectionView<ElemT, ViewT>> {
  @Override
  public PTransformReplacement<PCollection<ElemT>, PCollection<ElemT>> getReplacementTransform(
      AppliedPTransform<
              PCollection<ElemT>, PCollection<ElemT>, View.CreatePCollectionView<ElemT, ViewT>>
          transform) {

    @SuppressWarnings("unchecked")
    PCollection<ElemT> input =
        (PCollection<ElemT>) Iterables.getOnlyElement(transform.getInputs().values());

    return PTransformReplacement.of(
        input, new SamzaCreatePCollectionViewTransform<>(transform.getTransform().getView()));
  }

  private static class SamzaCreatePCollectionViewTransform<ElemT, ViewT>
      extends PTransform<PCollection<ElemT>, PCollection<ElemT>> {
    private final PCollectionView<ViewT> view;

    public SamzaCreatePCollectionViewTransform(PCollectionView<ViewT> view) {
      this.view = view;
    }

    @Override
    public PCollection<ElemT> expand(PCollection<ElemT> input) {
      // This actually creates a branch in the graph that publishes the view but then returns
      // the original input. This is copied from the Flink runner.
      input
          .apply(Combine.globally(new Concatenate<ElemT>()).withoutDefaults())
          .apply(new SamzaPublishView<>(view));
      return input;
    }
  }
}