1 /*
2 * ModeShape (http://www.modeshape.org)
3 * See the COPYRIGHT.txt file distributed with this work for information
4 * regarding copyright ownership. Some portions may be licensed
5 * to Red Hat, Inc. under one or more contributor license agreements.
6 * See the AUTHORS.txt file in the distribution for a full listing of
7 * individual contributors.
8 *
9 * ModeShape is free software. Unless otherwise indicated, all code in ModeShape
10 * is licensed to you under the terms of the GNU Lesser General Public License as
11 * published by the Free Software Foundation; either version 2.1 of
12 * the License, or (at your option) any later version.
13 *
14 * ModeShape is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
18 *
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this software; if not, write to the Free
21 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
22 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
23 */
24 package org.modeshape.graph.query.optimize;
25
26 import java.util.LinkedList;
27 import net.jcip.annotations.Immutable;
28 import org.modeshape.graph.query.QueryContext;
29 import org.modeshape.graph.query.plan.PlanNode;
30 import org.modeshape.graph.query.plan.PlanNode.Property;
31 import org.modeshape.graph.query.plan.PlanNode.Type;
32
33 /**
34 * An {@link OptimizerRule optimizer rule} that removes any ACCESS nodes that are known to never return any tuples because of
35 * conflicting constraints.
36 */
37 @Immutable
38 public class RemoveEmptyAccessNodes implements OptimizerRule {
39
40 public static final RemoveEmptyAccessNodes INSTANCE = new RemoveEmptyAccessNodes();
41
42 /**
43 * {@inheritDoc}
44 *
45 * @see org.modeshape.graph.query.optimize.OptimizerRule#execute(org.modeshape.graph.query.QueryContext,
46 * org.modeshape.graph.query.plan.PlanNode, java.util.LinkedList)
47 */
48 public PlanNode execute( QueryContext context,
49 PlanNode plan,
50 LinkedList<OptimizerRule> ruleStack ) {
51 // Find all access nodes ...
52 for (PlanNode access : plan.findAllAtOrBelow(Type.ACCESS)) {
53 if (access.getProperty(Property.ACCESS_NO_RESULTS, Boolean.class)) {
54 // This node has conflicting constraints and will never return any results ...
55
56 // TODO: implement this rule.
57
58 // At least the QueryProcessor looks for this property and always creates a NoResultsComponent,
59 // saving some work. But implementing this rule will make queries more efficient.
60 }
61 }
62
63 return plan;
64 }
65 }