io.mindmaps.graql.internal.gremlin.ShortcutTraversal Maven / Gradle / Ivy

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/*
 * MindmapsDB - A Distributed Semantic Database
 * Copyright (C) 2016  Mindmaps Research Ltd
 *
 * MindmapsDB is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * MindmapsDB is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with MindmapsDB. If not, see .
 */

package io.mindmaps.graql.internal.gremlin;

import org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal;
import org.apache.tinkerpop.gremlin.structure.Edge;
import org.apache.tinkerpop.gremlin.structure.Vertex;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import static io.mindmaps.util.Schema.EdgeLabel.SHORTCUT;
import static io.mindmaps.util.Schema.EdgeProperty.*;

/**
 * some {@code VarTraversals} can be represented using shortcut edges.
 * {@code ShortcutTraversal} represents this pattern in order to improve query performance
 * 
 * A {@code VarTraversals} can be represented by a shortcut edge when:
 * 

 *     it represents a relation
 *     the relation has no internal properties or resources specified (id, value ...)
 *     the relation has exactly two roleplayers
 *     if the type and role-types are specified, they are specified only by id and no other properties
 *     the relation has not been given a variable name
 * 
 */
public class ShortcutTraversal {

    private final List> roletypes = new ArrayList<>();
    private final List roleplayers = new ArrayList<>();
    private boolean valid = true;
    private Optional type = Optional.empty();
    private MultiTraversal multiTraversal = null;

    /**
     * @return true if a shortcut edge can be used in the traversal
     */
    boolean isValid() {
        return valid && (roleplayers.size() == 2);
    }

    /**
     * Make this ShortcutTraversal invalid, so it will not be used in the traversal
     */
    public void setInvalid() {
        valid = false;
    }

    /**
     * @return a MultiTraversal that follows shortcut edges
     */
    MultiTraversal getMultiTraversal() {
        if (multiTraversal == null) makeMultiTraversal();
        return multiTraversal;
    }

    /**
     * Create a MultiTraversal that follows shortcut edges
     */
    private void makeMultiTraversal() {
        Optional roleA = roletypes.get(0);
        String playerA = roleplayers.get(0);
        Optional roleB = roletypes.get(1);
        String playerB = roleplayers.get(1);

        multiTraversal = MultiTraversal.create(
                new FragmentImpl(t -> makeTraversal(t, roleA, roleB), FragmentPriority.EDGE_RELATION, playerA, playerB),
                new FragmentImpl(t -> makeTraversal(t, roleB, roleA), FragmentPriority.EDGE_RELATION, playerB, playerA)
        );
    }

    /**
     * @param traversal the traversal to start from
     * @param roleA the role type of A, if one is specified
     * @param roleB the role type of B, if one is specified
     * @return a traversal following a shortcut edge from A to B using the given roles
     */
    private GraphTraversal makeTraversal(
            GraphTraversal traversal, Optional roleA, Optional roleB
    ) {
        GraphTraversal edgeTraversal = traversal.outE(SHORTCUT.getLabel());
        roleA.ifPresent(ra -> edgeTraversal.has(FROM_ROLE.name(), ra));
        roleB.ifPresent(rb -> edgeTraversal.has(TO_ROLE.name(), rb));
        type.ifPresent(t -> edgeTraversal.has(RELATION_TYPE_ID.name(), t));
        return edgeTraversal.inV();
    }

    /**
     * @param type the type of the variable this ShortcutTraversal represents
     */
    public void setType(String type) {
        if (!this.type.isPresent()) {
            this.type = Optional.of(type);
        } else {
            setInvalid();
        }
    }

    /**
     * @param roleplayer a roleplayer of the relation that this ShortcutTraversal represents
     */
    public void addRel(String roleplayer) {
        roletypes.add(Optional.empty());
        roleplayers.add(roleplayer);
    }

    /**
     * @param roletype the role type of the given roleplayer
     * @param roleplayer a roleplayer of the relation that this ShortcutTraversal represents
     */
    public void addRel(String roletype, String roleplayer) {
        roletypes.add(Optional.of(roletype));
        roleplayers.add(roleplayer);
    }
}