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 }