001 /*
002 * Cumulus4j - Securing your data in the cloud - http://cumulus4j.org
003 * Copyright (C) 2011 NightLabs Consulting GmbH
004 *
005 * This program is free software: you can redistribute it and/or modify
006 * it under the terms of the GNU Affero General Public License as
007 * published by the Free Software Foundation, either version 3 of the
008 * License, or (at your option) any later version.
009 *
010 * This program is distributed in the hope that it will be useful,
011 * but WITHOUT ANY WARRANTY; without even the implied warranty of
012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
013 * GNU Affero General Public License for more details.
014 *
015 * You should have received a copy of the GNU Affero General Public License
016 * along with this program. If not, see <http://www.gnu.org/licenses/>.
017 */
018 package org.cumulus4j.store.query.eval;
019
020 import java.util.Set;
021
022 import org.cumulus4j.store.query.QueryEvaluator;
023 import org.datanucleus.query.expression.DyadicExpression;
024
025 /**
026 * <p>
027 * Evaluator handling "!" (negation).
028 * </p>
029 * <p>
030 * It is quite expensive to evaluate a negation (JDOQL "!") by first querying the normal (non-negated)
031 * result and then negating it by querying ALL candidates and finally filtering the normal result
032 * out. Therefore, we instead push the negation down the expression-evaluator-tree into the leafs.
033 * Thus <code>NotExpressionEvaluator</code> simply calls {@link ResultDescriptor#negate()} and passes the negated
034 * <code>ResultDescriptor</code> down the evaluator-tree. All nodes in the tree therefore have to take this
035 * negation-flag into account.
036 * </p>
037 * <p>
038 * Example 1: Instead of querying the expensive expression "!( a > 5 && b <= 12 )", the cheaper
039 * equivalent "a <= 5 || b > 12" is used.
040 * </p>
041 * <p>
042 * Example 2: Instead of "!( !( a > 5 && b <= 12 ) || c > 3 )" the equivalent "( a <= 5 || b > 12 ) && c <= 3"
043 * is executed.
044 * </p>
045 * <p>
046 * See <a target="_blank" href="http://en.wikipedia.org/wiki/De_Morgan%27s_laws">De Morgan's laws</a> in wikipedia for details.
047 * </p>
048 *
049 * @author Marco หงุ่ยตระกูล-Schulze - marco at nightlabs dot de
050 */
051 public class NotExpressionEvaluator extends AbstractExpressionEvaluator<DyadicExpression>
052 {
053 public NotExpressionEvaluator(QueryEvaluator queryEvaluator, AbstractExpressionEvaluator<?> parent, DyadicExpression expression)
054 {
055 super(queryEvaluator, parent, expression);
056 }
057
058 @Override
059 protected Set<Long> _queryResultDataEntryIDs(ResultDescriptor resultDescriptor)
060 {
061 if (getLeft() != null && getRight() != null)
062 throw new UnsupportedOperationException("Both left and right are assigned - one of them must be null!");
063
064 if (getLeft() != null)
065 return getLeft().queryResultDataEntryIDs(resultDescriptor.negate());
066
067 if (getRight() != null)
068 return getRight().queryResultDataEntryIDs(resultDescriptor.negate());
069
070 throw new UnsupportedOperationException("Both left and right are null - one of them must be assigned!");
071 }
072 }