| /* |
| * 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.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.filter.RangeGlobalStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.IdStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.LabelStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.OrderGlobalStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.PathStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.SackStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectOneStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.step.map.TreeStep; |
| import org.apache.tinkerpop.gremlin.process.traversal.strategy.AbstractTraversalStrategy; |
| import org.apache.tinkerpop.gremlin.process.traversal.util.TraversalHelper; |
| |
| import java.util.Arrays; |
| import java.util.HashSet; |
| import java.util.List; |
| import java.util.Set; |
| |
| /** |
| * @author Marko A. Rodriguez (http://markorodriguez.com) |
| */ |
| public final class OrderLimitStrategy extends AbstractTraversalStrategy<TraversalStrategy.OptimizationStrategy> implements TraversalStrategy.OptimizationStrategy { |
| |
| private static final OrderLimitStrategy INSTANCE = new OrderLimitStrategy(); |
| |
| private static Set<Class<? extends Step>> LEGAL_STEPS = new HashSet<>( |
| Arrays.asList(LabelStep.class, |
| IdStep.class, |
| PathStep.class, |
| SelectStep.class, |
| SelectOneStep.class, |
| SackStep.class, |
| TreeStep.class)); |
| |
| private OrderLimitStrategy() { |
| } |
| |
| @Override |
| public void apply(final Traversal.Admin<?, ?> traversal) { |
| if (!TraversalHelper.onGraphComputer(traversal)) |
| return; |
| |
| final List<OrderGlobalStep> orders = TraversalHelper.getStepsOfClass(OrderGlobalStep.class, traversal); |
| for (final OrderGlobalStep order : orders) { |
| RangeGlobalStep range = null; |
| Step<?, ?> currentStep = order.getNextStep(); |
| while (true) { |
| if (currentStep instanceof RangeGlobalStep) { |
| range = (RangeGlobalStep) currentStep; |
| break; |
| } else if (!LEGAL_STEPS.contains(currentStep.getClass())) |
| break; |
| else |
| currentStep = currentStep.getNextStep(); |
| } |
| if (null != range) |
| order.setLimit(range.getHighRange()); |
| } |
| } |
| |
| public static OrderLimitStrategy instance() { |
| return INSTANCE; |
| } |
| } |