SetOperatorBase.java

/*
 * Copyright © 2014 - 2021 Leipzig University (Database Research Group)
 *
 * Licensed 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
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.gradoop.flink.model.impl.operators.base;

import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.tuple.Tuple2;
import org.gradoop.common.model.api.entities.Edge;
import org.gradoop.common.model.api.entities.GraphHead;
import org.gradoop.common.model.api.entities.Vertex;
import org.gradoop.flink.model.api.epgm.BaseGraph;
import org.gradoop.flink.model.api.epgm.BaseGraphCollection;
import org.gradoop.flink.model.impl.functions.epgm.Id;
import org.gradoop.flink.model.impl.functions.epgm.SourceId;
import org.gradoop.flink.model.impl.functions.epgm.TargetId;
import org.gradoop.flink.model.impl.functions.graphcontainment.PairVertexWithGraphs;
import org.gradoop.flink.model.impl.functions.utils.LeftSide;
import org.gradoop.flink.model.impl.operators.base.functions.LeftJoin0OfTuple2;
import org.gradoop.flink.model.impl.operators.difference.Difference;
import org.gradoop.flink.model.impl.operators.intersection.Intersection;
import org.gradoop.flink.model.impl.operators.union.Union;
import org.gradoop.common.model.impl.id.GradoopId;

/**
 * Base class for set operations that share common methods to build vertex, edge and data sets.
 *
 * @see Difference
 * @see Intersection
 * @see Union
 *
 * @param <G> type of the graph head
 * @param <V> the vertex type
 * @param <E> the edge type
 * @param <LG> type of the base graph instance
 * @param <GC> type of the graph collection
 */
public abstract class SetOperatorBase<
  G extends GraphHead,
  V extends Vertex,
  E extends Edge,
  LG extends BaseGraph<G, V, E, LG, GC>,
  GC extends BaseGraphCollection<G, V, E, LG, GC>>
  extends BinaryCollectionToCollectionOperatorBase<G, V, E, LG, GC> {

  /**
   * Computes new vertices based on the new subgraphs. For each vertex, each
   * graph is collected in a flatMap function and then joined with the new
   * subgraph dataset.
   *
   * @param newGraphHeads graph dataset of the resulting graph collection
   * @return vertex set of the resulting graph collection
   */
  @Override
  protected DataSet<V> computeNewVertices(DataSet<G> newGraphHeads) {

    DataSet<Tuple2<V, GradoopId>> verticesWithGraphs =
      firstCollection.getVertices().flatMap(new PairVertexWithGraphs<>());

    return verticesWithGraphs
      .join(newGraphHeads)
      .where(1)
      .equalTo(new Id<>())
      .with(new LeftJoin0OfTuple2<>())
      .withForwardedFieldsFirst("f0->*")
      .distinct(new Id<>());
  }

  /**
   * Constructs new edges by joining the edges of the first graph with the new vertices.
   *
   * @param newVertices vertex set of the resulting graph collection
   * @return edges set only connect vertices in {@code newVertices}
   * @see Difference
   * @see Intersection
   */
  @Override
  protected DataSet<E> computeNewEdges(DataSet<V> newVertices) {
    return firstCollection.getEdges().join(newVertices)
      .where(new SourceId<>())
      .equalTo(new Id<>())
      .with(new LeftSide<>())
      .join(newVertices)
      .where(new TargetId<>())
      .equalTo(new Id<>())
      .with(new LeftSide<>())
      .distinct(new Id<>());
  }
}