| /* |
| * 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.step; |
| |
| import org.apache.tinkerpop.gremlin.process.traversal.Path; |
| import org.apache.tinkerpop.gremlin.process.traversal.Pop; |
| import org.apache.tinkerpop.gremlin.process.traversal.Step; |
| import org.apache.tinkerpop.gremlin.process.traversal.Traverser; |
| |
| import java.util.Map; |
| import java.util.Set; |
| |
| /** |
| * This interface is implemented by {@link Step} implementations that access labeled path steps, side-effects or |
| * {@code Map} values by key, such as {@code select('a')} step. Note that a step like {@code project()} is non-scoping |
| * because while it creates a {@code Map} it does not introspect them. |
| * <p/> |
| * There are four types of scopes: |
| * <ol> |
| * <li>Current scope</li> — the current data referenced by the traverser (“path head”). |
| * <li>Path scope</li> — a particular piece of data in the path of the traverser (“path history”). |
| * <li>Side-effect scope</li> — a particular piece of data in the global traversal blackboard. |
| * <li>Map scope</li> — a particular piece of data in the current scope map (“map value by key”). |
| * </ol> |
| * |
| * The current scope refers to the current object referenced by the traverser. That is, the {@code traverser.get()} |
| * object. Another way to think about the current scope is to think in terms of the path of the traverser where the |
| * current scope is the head of the path. With the math()-step, the variable {@code _} refers to the current scope. |
| * |
| * <pre> |
| * {@code |
| * gremlin> g.V().values("age").math("sin _") |
| * ==>-0.6636338842129675 |
| * ==>0.956375928404503 |
| * ==>0.5514266812416906 |
| * ==>-0.428182669496151 |
| * } |
| * </pre> |
| * |
| * The path scope refers to data previously seen by the traverser. That is, data in the traverser’s path history. |
| * Paths can be accessed by {@code path()}, however, individual parts of the path can be labeled using {@code as()} |
| * and accessed later via the path label name. Thus, in the traversal below, “a” and “b” refer to objects previously |
| * traversed by the traverser. |
| * |
| * <pre> |
| * {@code |
| * gremlin> g.V().as("a").out("knows").as("b”). |
| * math("a / b").by("age") |
| * ==>1.0740740740740742 |
| * ==>0.90625 |
| * } |
| * </pre> |
| * |
| * The side-effect scope refers objects in the global side-effects of the traversal. Side-effects are not local to the |
| * traverser, but instead, global to the traversal. In the traversal below you can see how “x” is being referenced in |
| * the math()-step and thus, the side-effect data is being used. |
| * |
| * <pre> |
| * {@code |
| * gremlin> g.withSideEffect("x",100).V().values("age").math("_ / x") |
| * ==>0.29 |
| * ==>0.27 |
| * ==>0.32 |
| * ==>0.35 |
| * } |
| * </pre> |
| * |
| * Map scope refers to objects within the current map object. Thus, its like current scope, but a bit “deeper.” In the |
| * traversal below the {@code project()}-step generates a map with keys “a” and “b”. The subsequent {@code math()}-step |
| * is then able to access the “a” and “b” values in the respective map and use them for the division operation. |
| * |
| * <pre> |
| * {@code gremlin> |
| * g.V().hasLabel("person”). |
| * project("a","b”). |
| * by("age”). |
| * by(bothE().count()). |
| * math("a / b") |
| * ==>9.666666666666666 |
| * ==>27.0 |
| * ==>10.666666666666666 |
| * ==>35.0 |
| * } |
| * </pre> |
| * |
| * Scoping is all about variable data access and forms the fundamental interface for access to the memory structures |
| * of Gremlin. |
| * |
| * @author Marko A. Rodriguez (http://markorodriguez.com) |
| * @author Stephen Mallette (http://stephen.genoprime.com) |
| */ |
| public interface Scoping { |
| |
| public enum Variable {START, END} |
| |
| /** |
| * Finds the object with the specified key for the current traverser and throws an exception if the key cannot |
| * be found. |
| * |
| * @throws KeyNotFoundException if the key does not exist |
| */ |
| public default <S> S getScopeValue(final Pop pop, final Object key, final Traverser.Admin<?> traverser) throws KeyNotFoundException { |
| final Object object = traverser.get(); |
| if (object instanceof Map && ((Map) object).containsKey(key)) |
| return (S) ((Map) object).get(key); |
| |
| if (key instanceof String) { |
| final String k = (String) key; |
| if (traverser.getSideEffects().exists(k)) |
| return traverser.getSideEffects().get(k); |
| |
| final Path path = traverser.path(); |
| if (path.hasLabel(k)) |
| return null == pop ? path.get(k) : path.get(pop, k); |
| } |
| |
| throw new KeyNotFoundException(key, this); |
| } |
| |
| /** |
| * Calls {@link #getScopeValue(Pop, Object, Traverser.Admin)} but throws an unchecked {@code IllegalStateException} |
| * if the key cannot be found. |
| */ |
| public default <S> S getSafeScopeValue(final Pop pop, final Object key, final Traverser.Admin<?> traverser) { |
| try { |
| return getScopeValue(pop, key, traverser); |
| } catch (KeyNotFoundException nfe) { |
| throw new IllegalArgumentException(nfe.getMessage(), nfe); |
| } |
| } |
| |
| /** |
| * Calls {@link #getScopeValue(Pop, Object, Traverser.Admin)} and returns {@code null} if the key is not found. |
| * Use this method with caution as {@code null} has one of two meanings as a return value. It could be that the |
| * key was found and its value was {@code null} or it might mean that the key was not found and {@code null} was |
| * simply returned. |
| */ |
| public default <S> S getNullableScopeValue(final Pop pop, final String key, final Traverser.Admin<?> traverser) { |
| try { |
| return getScopeValue(pop, key, traverser); |
| } catch (KeyNotFoundException nfe) { |
| return null; |
| } |
| } |
| |
| /** |
| * Get the labels that this scoping step will access during the traversal |
| * |
| * @return the accessed labels of the scoping step |
| */ |
| public Set<String> getScopeKeys(); |
| |
| public static class KeyNotFoundException extends Exception { |
| |
| private final Object key; |
| private final Scoping step; |
| |
| public KeyNotFoundException(final Object key, final Scoping current) { |
| super("Neither the map, sideEffects, nor path has a " + key + "-key: " + current); |
| this.key = key; |
| this.step = current; |
| } |
| |
| public Object getKey() { |
| return key; |
| } |
| |
| public Scoping getStep() { |
| return step; |
| } |
| } |
| } |