/*
* 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 org.modeshape.common.annotation.Immutable;
import org.modeshape.jcr.query.QueryContext;
import org.modeshape.jcr.query.model.JoinType;
import org.modeshape.jcr.query.plan.PlanNode;
import org.modeshape.jcr.query.plan.PlanNode.Property;
import org.modeshape.jcr.query.plan.PlanNode.Type;
/**
* An {@link OptimizerRule optimizer rule} that converts {@link JoinType#RIGHT_OUTER right outer joins} into
* {@link JoinType#LEFT_OUTER left outer joins}.
*/
@Immutable
public class RightOuterToLeftOuterJoins implements OptimizerRule {
public static final RightOuterToLeftOuterJoins INSTANCE = new RightOuterToLeftOuterJoins();
@Override
public PlanNode execute( QueryContext context,
PlanNode plan,
LinkedList<OptimizerRule> ruleStack ) {
// For each of the JOIN nodes ...
for (PlanNode joinNode : plan.findAllAtOrBelow(Type.JOIN)) {
if (JoinType.RIGHT_OUTER == joinNode.getProperty(Property.JOIN_TYPE, JoinType.class)) {
// Swap the information ...
PlanNode left = joinNode.getFirstChild();
left.removeFromParent(); // right is now the first child ...
left.setParent(joinNode);
joinNode.setProperty(Property.JOIN_TYPE, JoinType.LEFT_OUTER);
// None of the Constraints or JoinCondition need to be changed (they refer to named selectors) ...
}
}
return plan;
}
@Override
public String toString() {
return getClass().getSimpleName();
}
}