runners/spark/3/src/main/java/org/apache/beam/runners/spark/structuredstreaming/translation/batch/FlattenTranslatorBatch.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
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.beam.runners.spark.structuredstreaming.translation.batch;

import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkArgument;

import java.util.Collection;
import org.apache.beam.runners.spark.structuredstreaming.translation.AbstractTranslationContext;
import org.apache.beam.runners.spark.structuredstreaming.translation.TransformTranslator;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.util.WindowedValue;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.PCollectionList;
import org.apache.beam.sdk.values.PValue;
import org.apache.spark.sql.Dataset;

@SuppressWarnings({
  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
})
class FlattenTranslatorBatch<T>
    implements TransformTranslator<PTransform<PCollectionList<T>, PCollection<T>>> {

  @Override
  public void translateTransform(
      PTransform<PCollectionList<T>, PCollection<T>> transform,
      AbstractTranslationContext context) {
    Collection<PCollection<?>> pcollectionList = context.getInputs().values();
    Dataset<WindowedValue<T>> result = null;
    if (pcollectionList.isEmpty()) {
      result = context.emptyDataset();
    } else {
      for (PValue pValue : pcollectionList) {
        checkArgument(
            pValue instanceof PCollection,
            "Got non-PCollection input to flatten: %s of type %s",
            pValue,
            pValue.getClass().getSimpleName());
        @SuppressWarnings("unchecked")
        PCollection<T> pCollection = (PCollection<T>) pValue;
        Dataset<WindowedValue<T>> current = context.getDataset(pCollection);
        if (result == null) {
          result = current;
        } else {
          result = result.union(current);
        }
      }
    }
    context.putDataset(context.getOutput(), result);
  }
}