/*
* $Header$
* $Revision: 3132 $
* $Date: 2009-10-04 12:20:14 +1000 (Sun, 04 Oct 2009) $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 2003-2009 The JRDF Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The JRDF Project" and "JRDF" must not be used to endorse
* or promote products derived from this software without prior written
* permission. For written permission, please contact
* newmana@users.sourceforge.net.
*
* 5. Products derived from this software may not be called "JRDF"
* nor may "JRDF" appear in their names without prior written
* permission of the JRDF Project.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the JRDF Project. For more
* information on JRDF, please see <http://jrdf.sourceforge.net/>.
*
*/
package org.jrdf.query.relation.operation.mem.join;
import org.jrdf.query.relation.EvaluatedRelation;
import static org.jrdf.query.relation.constants.RelationDEE.RELATION_DEE;
import static org.jrdf.query.relation.constants.RelationDUM.RELATION_DUM;
import org.jrdf.query.relation.operation.NadicJoin;
import org.jrdf.query.relation.operation.mem.common.RelationProcessor;
import java.util.Collections;
import java.util.Set;
/**
* A simple memory based implementation of NadicJoin.
*
* @author Andrew Newman
* @version $Revision: 3132 $
*/
public final class NadicJoinImpl implements NadicJoin {
private final TupleEngine tupleEngine;
private final RelationProcessor relationProcessor;
public NadicJoinImpl(RelationProcessor newRelationProcessor, TupleEngine newTupleEngine) {
this.tupleEngine = newTupleEngine;
this.relationProcessor = newRelationProcessor;
}
public EvaluatedRelation join(Set<EvaluatedRelation> relations) {
EvaluatedRelation relation = isDeeDumOrSingle(relations);
if (relation == null) {
relation = relationProcessor.processRelations(relations, tupleEngine);
}
return relation;
}
private EvaluatedRelation isDeeDumOrSingle(Set<EvaluatedRelation> relations) {
EvaluatedRelation relation = null;
// Is it the empty collection return DEE.
if (relations.equals(Collections.<EvaluatedRelation>emptySet())) {
relation = RELATION_DEE;
}
// Is it DUM - therefore return DUM
if (relations.contains(RELATION_DUM)) {
relation = RELATION_DUM;
}
// If relations contains DEE, remove it and return the rest of the set.
if (relations.contains(RELATION_DEE) && relations.size() > 1) {
relations.remove(RELATION_DEE);
}
// Is it just one relations - if so just return it back.
if (relations.size() == 1) {
relation = relations.iterator().next();
}
return relation;
}
}