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* Licensed to the Apache Software Foundation (ASF) under one
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* 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
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* 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.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.TraversalParent;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.ConnectiveStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.NotStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.RangeGlobalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.TraversalFilterStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.filter.WhereTraversalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.CountGlobalStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.PropertiesStep;
import org.apache.tinkerpop.gremlin.process.traversal.step.map.VertexStep;
import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy;
import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper;
import org.apache.tinkerpop.gremlin.structure.Edge;
import org.apache.tinkerpop.gremlin.structure.PropertyType;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* This strategy looks for vertex- and value-emitting steps followed by a {@link CountGlobalStep} and replaces the
* pattern with an edge- or property-emitting step followed by a {@code CountGlobalStep}. Furthermore, if a vertex-
* or value-emitting step is the last step in a {@code .has(traversal)}, {@code .and(traversal, ...)} or
* {@code .or(traversal, ...)} child traversal, it is replaced by an appropriate edge- or property-emitting step.
* <p/>
*
* @author Daniel Kuppitz (http://gremlin.guru)
* @example <pre>
* __.out().count() // is replaced by __.outE().count()
* __.in().limit(3).count() // is replaced by __.inE().limit(3).count()
* __.values("name").count() // is replaced by __.properties("name").count()
* __.where(__.out()) // is replaced by __.where(__.outE())
* __.where(__.values()) // is replaced by __.where(__.properties())
* __.and(__.in(), __.out()) // is replaced by __.and(__.inE(), __.outE())
* </pre>
*/
public final class AdjacentToIncidentStrategy extends AbstractTraversalStrategy<TraversalStrategy.OptimizationStrategy>
implements TraversalStrategy.OptimizationStrategy {
private static final AdjacentToIncidentStrategy INSTANCE = new AdjacentToIncidentStrategy();
private static final Set<Class<? extends OptimizationStrategy>> PRIORS = new HashSet<>(Arrays.asList(IdentityRemovalStrategy.class, IncidentToAdjacentStrategy.class));
private AdjacentToIncidentStrategy() {
}
@Override
public void apply(final Traversal.Admin<?, ?> traversal) {
final List<Step> steps = traversal.getSteps();
final int size = steps.size() - 1;
Step prev = null;
for (int i = 0; i <= size; i++) {
final Step curr = steps.get(i);
if (i == size && isOptimizable(curr)) {
final TraversalParent parent = curr.getTraversal().getParent();
if (parent instanceof NotStep || parent instanceof TraversalFilterStep || parent instanceof WhereTraversalStep || parent instanceof ConnectiveStep) {
optimizeStep(traversal, curr);
}
} else if (isOptimizable(prev)) {
if (curr instanceof CountGlobalStep) {
optimizeStep(traversal, prev);
}
}
if (!(curr instanceof RangeGlobalStep)) {
prev = curr;
}
}
}
@Override
public Set<Class<? extends OptimizationStrategy>> applyPrior() {
return PRIORS;
}
/**
* Checks whether a given step is optimizable or not.
*
* @param step the step to check
* @return <code>true</code> if the step is optimizable, otherwise <code>false</code>
*/
private static boolean isOptimizable(final Step step) {
return ((step instanceof VertexStep && ((VertexStep) step).returnsVertex()) ||
(step instanceof PropertiesStep && PropertyType.VALUE.equals(((PropertiesStep) step).getReturnType()))) && (step.getTraversal().getEndStep().getLabels().isEmpty() || step.getNextStep() instanceof CountGlobalStep);
}
/**
* Optimizes the given step if possible. Basically this method converts <code>.out()</code> to <code>.outE()</code>
* and <code>.values()</code> to <code>.properties()</code>.
*
* @param traversal the traversal that holds the given step
* @param step the step to replace
*/
private static void optimizeStep(final Traversal.Admin traversal, final Step step) {
final Step newStep;
if (step instanceof VertexStep) {
final VertexStep vs = (VertexStep) step;
newStep = new VertexStep<>(traversal, Edge.class, vs.getDirection(), vs.getEdgeLabels());
} else if (step instanceof PropertiesStep) {
final PropertiesStep ps = (PropertiesStep) step;
newStep = new PropertiesStep(traversal, PropertyType.PROPERTY, ps.getPropertyKeys());
} else {
return;
}
TraversalHelper.replaceStep(step, newStep, traversal);
}
public static AdjacentToIncidentStrategy instance() {
return INSTANCE;
}
}