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1   /*
2    * ModeShape (http://www.modeshape.org)
3    * See the COPYRIGHT.txt file distributed with this work for information
4    * regarding copyright ownership.  Some portions may be licensed
5    * to Red Hat, Inc. under one or more contributor license agreements.
6    * See the AUTHORS.txt file in the distribution for a full listing of 
7    * individual contributors.
8    *
9    * ModeShape is free software. Unless otherwise indicated, all code in ModeShape
10   * is licensed to you under the terms of the GNU Lesser General Public License as
11   * published by the Free Software Foundation; either version 2.1 of
12   * the License, or (at your option) any later version.
13   * 
14   * ModeShape is distributed in the hope that it will be useful,
15   * but WITHOUT ANY WARRANTY; without even the implied warranty of
16   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17   * Lesser General Public License for more details.
18   *
19   * You should have received a copy of the GNU Lesser General Public
20   * License along with this software; if not, write to the Free
21   * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
22   * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
23   */
24  package org.modeshape.graph.query.optimize;
25  
26  import java.util.LinkedList;
27  import net.jcip.annotations.Immutable;
28  import org.modeshape.graph.query.QueryContext;
29  import org.modeshape.graph.query.plan.CanonicalPlanner;
30  import org.modeshape.graph.query.plan.PlanHints;
31  import org.modeshape.graph.query.plan.PlanNode;
32  import org.modeshape.graph.query.plan.PlanNode.Type;
33  
34  /**
35   * An {@link OptimizerRule optimizer rule} that inserts an ACCESS above each SOURCE leaf node in a query plan. This rule is often
36   * the first rule to run against a {@link CanonicalPlanner canonical plan} (see
37   * {@link RuleBasedOptimizer#populateRuleStack(LinkedList, PlanHints)}.
38   * <p>
39   * Before:
40   * 
41   * <pre>
42   *        ...
43   *         |
44   *       SOURCE
45   * </pre>
46   * 
47   * After:
48   * 
49   * <pre>
50   *        ...
51   *         |
52   *       ACCESS
53   *         |
54   *       SOURCE
55   * </pre>
56   * 
57   * </p>
58   */
59  @Immutable
60  public class AddAccessNodes implements OptimizerRule {
61  
62      public static final AddAccessNodes INSTANCE = new AddAccessNodes();
63  
64      /**
65       * {@inheritDoc}
66       * 
67       * @see org.modeshape.graph.query.optimize.OptimizerRule#execute(org.modeshape.graph.query.QueryContext,
68       *      org.modeshape.graph.query.plan.PlanNode, java.util.LinkedList)
69       */
70      public PlanNode execute( QueryContext context,
71                               PlanNode plan,
72                               LinkedList<OptimizerRule> ruleStack ) {
73          // On each of the source nodes ...
74          for (PlanNode source : plan.findAllAtOrBelow(Type.SOURCE)) {
75              // The source node may have children if it is a view ...
76              if (source.getChildCount() != 0) continue;
77  
78              // Create the ACCESS node, set the selectors, and insert above the source node ...
79              PlanNode access = new PlanNode(Type.ACCESS);
80              access.addSelectors(source.getSelectors());
81              source.insertAsParent(access);
82          }
83          return plan;
84      }
85  
86      /**
87       * {@inheritDoc}
88       * 
89       * @see java.lang.Object#toString()
90       */
91      @Override
92      public String toString() {
93          return getClass().getSimpleName();
94      }
95  
96  }