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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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
*
* 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.apache.tinkerpop.gremlin.process.traversal.strategy.optimization;
import org.apache.tinkerpop.gremlin.process.computer.traversal.step.map.VertexProgramStep;
import org.apache.tinkerpop.gremlin.process.traversal.Step;
import org.apache.tinkerpop.gremlin.process.traversal.Traversal;
import org.apache.tinkerpop.gremlin.process.traversal.TraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.step.LambdaHolder;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.PathFilterStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.EdgeOtherVertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.EdgeVertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.PathStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.TreeStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.VertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.TreeSideEffectStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.util.EmptyStep;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
import org.apache.tinkerpop.gremlin.structure.Direction;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.Vertex;
import org.javatuples.Pair;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
/**
* This strategy looks for {@code .outE().inV()}, {@code .inE().outV()} and {@code .bothE().otherV()}
* and replaces these step sequences with {@code .out()}, {@code .in()} or {@code .both()} respectively.
* The strategy won't modify the traversal if:
* <ul>
* <li>the edge step is labeled</li>
* <li>the traversal contains a {@code path} step</li>
* <li>the traversal contains a lambda step</li>
* </ul>
* <p/>
*
* @author Daniel Kuppitz (http://gremlin.guru)
* @example <pre>
* __.outE().inV() // is replaced by __.out()
* __.inE().outV() // is replaced by __.in()
* __.bothE().otherV() // is replaced by __.both()
* __.bothE().bothV() // will not be modified
* __.outE().inV().path() // will not be modified
* __.outE().inV().tree() // will not be modified
* </pre>
*/
public final class IncidentToAdjacentStrategy extends AbstractTraversalStrategy<TraversalStrategy.OptimizationStrategy>
implements TraversalStrategy.OptimizationStrategy {
private static final IncidentToAdjacentStrategy INSTANCE = new IncidentToAdjacentStrategy();
private static final String MARKER = Graph.Hidden.hide("gremlin.incidentToAdjacent");
private static final Set<Class> INVALIDATING_STEP_CLASSES = new HashSet<>(Arrays.asList(
PathStep.class, PathFilterStep.class, TreeStep.class, TreeSideEffectStep.class, LambdaHolder.class));
private IncidentToAdjacentStrategy() {
}
/**
* Checks whether a given step is optimizable or not.
*
* @param step1 an edge-emitting step
* @param step2 a vertex-emitting step
* @return <code>true</code> if step1 is not labeled and emits edges and step2 emits vertices,
* otherwise <code>false</code>
*/
private static boolean isOptimizable(final Step step1, final Step step2) {
if (step1 instanceof VertexStep && ((VertexStep) step1).returnsEdge() && step1.getLabels().isEmpty()) {
final Direction step1Dir = ((VertexStep) step1).getDirection();
if (step1Dir.equals(Direction.BOTH)) {
return step2 instanceof EdgeOtherVertexStep;
}
return step2 instanceof EdgeOtherVertexStep || (step2 instanceof EdgeVertexStep &&
((EdgeVertexStep) step2).getDirection().equals(step1Dir.opposite()));
}
return false;
}
/**
* Optimizes the given edge-emitting step and the vertex-emitting step by replacing them with a single
* vertex-emitting step.
*
* @param traversal the traversal that holds the given steps
* @param step1 the edge-emitting step to replace
* @param step2 the vertex-emitting step to replace
*/
private static void optimizeSteps(final Traversal.Admin traversal, final VertexStep step1, final Step step2) {
final Step newStep = new VertexStep(traversal, Vertex.class, step1.getDirection(), step1.getEdgeLabels());
for (final String label : (Iterable<String>) step2.getLabels()) {
newStep.addLabel(label);
}
TraversalHelper.replaceStep(step1, newStep, traversal);
traversal.removeStep(step2);
}
public static IncidentToAdjacentStrategy instance() {
return INSTANCE;
}
@Override
public void apply(final Traversal.Admin<?, ?> traversal) {
// using a hidden label marker to denote whether the traversal should not be processed by this strategy
if ((traversal.getParent() instanceof EmptyStep || traversal.getParent() instanceof VertexProgramStep) &&
TraversalHelper.hasStepOfAssignableClassRecursively(INVALIDATING_STEP_CLASSES, traversal))
TraversalHelper.applyTraversalRecursively(t -> t.getStartStep().addLabel(MARKER), traversal);
if (traversal.getStartStep().getLabels().contains(MARKER)) {
traversal.getStartStep().removeLabel(MARKER);
return;
}
////////////////////////////////////////////////////////////////////////////
final Collection<Pair<VertexStep, Step>> stepsToReplace = new ArrayList<>();
Step prev = null;
for (final Step curr : traversal.getSteps()) {
if (isOptimizable(prev, curr)) {
stepsToReplace.add(Pair.with((VertexStep) prev, curr));
}
prev = curr;
}
if (!stepsToReplace.isEmpty()) {
for (final Pair<VertexStep, Step> pair : stepsToReplace) {
optimizeSteps(traversal, pair.getValue0(), pair.getValue1());
}
}
}
@Override
public Set<Class<? extends OptimizationStrategy>> applyPrior() {
return Collections.singleton(IdentityRemovalStrategy.class);
}
}