/*
* JBoss DNA (http://www.jboss.org/dna)
* See the COPYRIGHT.txt file distributed with this work for information
* regarding copyright ownership. Some portions may be licensed
* to Red Hat, Inc. under one or more contributor license agreements.
* See the AUTHORS.txt file in the distribution for a full listing of
* individual contributors.
*
* JBoss DNA is free software. Unless otherwise indicated, all code in JBoss DNA
* is licensed to you under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* JBoss DNA is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/
package org.jboss.dna.graph.query.optimize;
import java.util.LinkedList;
import net.jcip.annotations.Immutable;
import org.jboss.dna.graph.query.QueryContext;
import org.jboss.dna.graph.query.plan.CanonicalPlanner;
import org.jboss.dna.graph.query.plan.PlanHints;
import org.jboss.dna.graph.query.plan.PlanNode;
import org.jboss.dna.graph.query.plan.PlanNode.Type;
/**
* An {@link OptimizerRule optimizer rule} that inserts an ACCESS above each SOURCE leaf node in a query plan. This rule is often
* the first rule to run against a {@link CanonicalPlanner canonical plan} (see
* {@link RuleBasedOptimizer#populateRuleStack(LinkedList, PlanHints)}.
* <p>
* Before:
*
* <pre>
* ...
* |
* SOURCE
* </pre>
*
* After:
*
* <pre>
* ...
* |
* ACCESS
* |
* SOURCE
* </pre>
*
* </p>
*/
@Immutable
public class AddAccessNodes implements OptimizerRule {
public static final AddAccessNodes INSTANCE = new AddAccessNodes();
/**
* {@inheritDoc}
*
* @see org.jboss.dna.graph.query.optimize.OptimizerRule#execute(org.jboss.dna.graph.query.QueryContext,
* org.jboss.dna.graph.query.plan.PlanNode, java.util.LinkedList)
*/
public PlanNode execute( QueryContext context,
PlanNode plan,
LinkedList<OptimizerRule> ruleStack ) {
// On each of the source nodes ...
for (PlanNode source : plan.findAllAtOrBelow(Type.SOURCE)) {
// The source node may have children if it is a view ...
if (source.getChildCount() != 0) continue;
// Create the ACCESS node, set the selectors, and insert above the source node ...
PlanNode access = new PlanNode(Type.ACCESS);
access.addSelectors(source.getSelectors());
source.insertAsParent(access);
}
return plan;
}
/**
* {@inheritDoc}
*
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return getClass().getSimpleName();
}
}