/*
* ModeShape (http://www.modeshape.org)
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.modeshape.jcr.query.optimize;
import java.util.LinkedList;
import javax.jcr.query.qom.JoinCondition;
import org.modeshape.jcr.query.QueryContext;
import org.modeshape.jcr.query.model.ChildNodeJoinCondition;
import org.modeshape.jcr.query.model.DescendantNodeJoinCondition;
import org.modeshape.jcr.query.model.JoinType;
import org.modeshape.jcr.query.model.SelectorName;
import org.modeshape.jcr.query.plan.PlanNode;
import org.modeshape.jcr.query.plan.PlanNode.Property;
import org.modeshape.jcr.query.plan.PlanNode.Type;
/**
* An optimization rule that ensure that the order of the left and right side of a JOIN match certain join criteria, including
* {@link DescendantNodeJoinCondition} and {@link ChildNodeJoinCondition}.
*
* @author Randall Hauch (rhauch@redhat.com)
*/
public class JoinOrder implements OptimizerRule {
public static final JoinOrder INSTANCE = new JoinOrder();
@Override
public PlanNode execute( final QueryContext context,
PlanNode plan,
LinkedList<OptimizerRule> ruleStack ) {
for (PlanNode join : plan.findAllAtOrBelow(Type.JOIN)) {
boolean swapChildren = false;
JoinCondition joinCondition = join.getProperty(Property.JOIN_CONDITION, JoinCondition.class);
if (joinCondition instanceof DescendantNodeJoinCondition) {
DescendantNodeJoinCondition condition = (DescendantNodeJoinCondition)joinCondition;
SelectorName ancestorSelector = condition.ancestorSelectorName();
// The ancestor needs to be on the left side of the join ...
swapChildren = !join.getFirstChild().getSelectors().contains(ancestorSelector);
} else if (joinCondition instanceof ChildNodeJoinCondition) {
ChildNodeJoinCondition condition = (ChildNodeJoinCondition)joinCondition;
SelectorName parentSelector = condition.parentSelectorName();
// The ancestor needs to be on the left side of the join ...
swapChildren = !join.getFirstChild().getSelectors().contains(parentSelector);
}
JoinType joinType = join.getProperty(Property.JOIN_TYPE, JoinType.class);
if (swapChildren) {
PlanNode first = join.getFirstChild();
first.removeFromParent();
join.addLastChild(first);
if (joinType == JoinType.LEFT_OUTER){
//we've reversed an outer join, so we need to change the join type
join.setProperty(Property.JOIN_TYPE, JoinType.RIGHT_OUTER);
} else if (joinType == JoinType.RIGHT_OUTER) {
//we've reversed an outer join, so we need to change the join type
join.setProperty(Property.JOIN_TYPE, JoinType.LEFT_OUTER);
}
}
}
return plan;
}
}