/*
* 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
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* 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,
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* 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
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package org.jboss.dna.graph.query.optimize;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import net.jcip.annotations.Immutable;
import org.jboss.dna.graph.GraphI18n;
import org.jboss.dna.graph.query.QueryContext;
import org.jboss.dna.graph.query.model.Column;
import org.jboss.dna.graph.query.model.EquiJoinCondition;
import org.jboss.dna.graph.query.model.JoinCondition;
import org.jboss.dna.graph.query.model.SameNodeJoinCondition;
import org.jboss.dna.graph.query.model.SelectorName;
import org.jboss.dna.graph.query.plan.PlanNode;
import org.jboss.dna.graph.query.plan.PlanUtil;
import org.jboss.dna.graph.query.plan.PlanNode.Property;
import org.jboss.dna.graph.query.plan.PlanNode.Type;
import org.jboss.dna.graph.query.validate.Schemata;
import org.jboss.dna.graph.query.validate.Schemata.Table;
/**
* An {@link OptimizerRule optimizer rule} that rewrites JOIN nodes that have {@link EquiJoinCondition equi-join criteria} where
* the columns involved in the equi-join are all identity columns (that is, they form a {@link Schemata.Table#getKeys() key} for
* the table). This rewrite only happens when the left and right children of the JOIN node are both SOURCE nodes.
* <p>
* The basic idea is that in these identity equi-join cases, the following structure:
*
* <pre>
* ...
* |
* JOIN
* / \
* / \
* SOURCE SOURCE
* </pre>
*
* is transformed into a simple SOURCE node:
*
* <pre>
* ...
* |
* SOURCE
* </pre>
*
* Note that this rewriting removes a selector, and thus the nodes above the JOIN node that made use of the removed selector are
* also modified to reference the remaining selector.
* </p>
*/
@Immutable
public class RewriteIdentityJoins implements OptimizerRule {
public static final RewriteIdentityJoins INSTANCE = new RewriteIdentityJoins();
/**
* {@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 ) {
if (!context.getHints().hasJoin) return plan;
// For each of the JOIN nodes ...
Map<SelectorName, SelectorName> rewrittenSelectors = null;
int rewrittenJoins = 0;
int numJoins = 0;
for (PlanNode joinNode : plan.findAllAtOrBelow(Type.JOIN)) {
++numJoins;
JoinCondition condition = joinNode.getProperty(Property.JOIN_CONDITION, JoinCondition.class);
if (condition instanceof EquiJoinCondition) {
PlanNode leftNode = joinNode.getFirstChild().findAtOrBelow(Type.SOURCE);
PlanNode rightNode = joinNode.getLastChild().findAtOrBelow(Type.SOURCE);
assert leftNode != null;
assert rightNode != null;
EquiJoinCondition equiJoin = (EquiJoinCondition)condition;
// Find the names (or aliases) of the tables ...
Schemata schemata = context.getSchemata();
assert schemata != null;
SelectorName leftTableName = leftNode.getProperty(Property.SOURCE_NAME, SelectorName.class);
SelectorName rightTableName = rightNode.getProperty(Property.SOURCE_NAME, SelectorName.class);
assert leftTableName != null;
assert rightTableName != null;
// Presumably the join condition is using at least one alias, but we only care about the actual name ...
if (!leftTableName.equals(rightTableName)) {
// The join is not joining the same table, so this doesn't meet the condition ...
continue;
}
// Find the schemata columns referenced by the join condition ...
Table table = schemata.getTable(leftTableName);
if (table == null) {
context.getProblems().addError(GraphI18n.tableDoesNotExist, leftTableName);
continue;
}
String leftColumnName = equiJoin.getProperty1Name();
String rightColumnName = equiJoin.getProperty2Name();
Schemata.Column leftColumn = table.getColumn(leftColumnName);
Schemata.Column rightColumn = table.getColumn(rightColumnName);
if (leftColumn == null) {
context.getProblems().addError(GraphI18n.columnDoesNotExistOnTable, leftColumnName, leftTableName);
continue;
}
if (rightColumn == null) {
context.getProblems().addError(GraphI18n.columnDoesNotExistOnTable, rightColumnName, leftTableName);
continue;
}
// Are the join columns (on both sides) keys?
if (table.hasKey(leftColumn) && (rightColumn == leftColumn || table.hasKey(rightColumn))) {
// It meets all the criteria, so rewrite this join node ...
if (rewrittenSelectors == null) rewrittenSelectors = new HashMap<SelectorName, SelectorName>();
rewriteJoinNode(context, joinNode, rewrittenSelectors);
++rewrittenJoins;
}
} else if (condition instanceof SameNodeJoinCondition) {
SameNodeJoinCondition sameNodeCondition = (SameNodeJoinCondition)condition;
if (sameNodeCondition.getSelector1Name().equals(sameNodeCondition.getSelector2Name())
&& sameNodeCondition.getSelector2Path() == null) {
// It meets all the criteria, so rewrite this join node ...
if (rewrittenSelectors == null) rewrittenSelectors = new HashMap<SelectorName, SelectorName>();
rewriteJoinNode(context, joinNode, rewrittenSelectors);
++rewrittenJoins;
}
}
}
if (rewrittenSelectors != null && !rewrittenSelectors.isEmpty()) {
// We re-wrote at least one JOIN, but since this only applies to JOIN nodes that meet certain criteria,
// the rewriting may have changed JOIN nodes that did not meet this criteria into nodes that now meet
// this criteria, so we need to re-run this rule...
ruleStack.addFirst(this);
// After this rule is done as is no longer needed, we need to try to push SELECTs and PROJECTs again ...
if (!(ruleStack.peek() instanceof PushSelectCriteria)) {
// We haven't already added these, so add them now ...
ruleStack.addFirst(PushProjects.INSTANCE);
if (context.getHints().hasCriteria) {
ruleStack.addFirst(PushSelectCriteria.INSTANCE);
}
}
// Now rewrite the various portions of the plan that make use of the now-removed selectors ...
PlanUtil.replaceReferencesToRemovedSource(context, plan, rewrittenSelectors);
assert rewrittenJoins > 0;
if (rewrittenJoins == numJoins) {
assert plan.findAllAtOrBelow(Type.JOIN).isEmpty();
context.getHints().hasJoin = false;
}
}
return plan;
}
protected void rewriteJoinNode( QueryContext context,
PlanNode joinNode,
Map<SelectorName, SelectorName> rewrittenSelectors ) {
// Remove the right source node from the join node ...
PlanNode rightChild = joinNode.getLastChild();
rightChild.removeFromParent();
PlanNode rightSource = rightChild.findAtOrBelow(Type.SOURCE);
// Replace the join node with the left source node ...
PlanNode leftChild = joinNode.getFirstChild();
joinNode.extractFromParent();
PlanNode leftSource = leftChild.findAtOrBelow(Type.SOURCE);
// Combine the right PROJECT node with that on the left ...
PlanNode rightProject = rightChild.findAtOrBelow(Type.PROJECT);
if (rightProject != null) {
PlanNode leftProject = leftChild.findAtOrBelow(Type.PROJECT);
if (leftProject != null) {
List<Column> leftColumns = leftProject.getPropertyAsList(Property.PROJECT_COLUMNS, Column.class);
for (Column rightColumn : rightProject.getPropertyAsList(Property.PROJECT_COLUMNS, Column.class)) {
if (!leftColumns.contains(rightColumn)) leftColumns.add(rightColumn);
}
} else {
// Just create a project on the left side ...
leftProject = new PlanNode(Type.PROJECT);
leftProject.setProperty(Property.PROJECT_COLUMNS, rightProject.getProperty(Property.PROJECT_COLUMNS));
leftChild.getFirstChild().insertAsParent(leftProject);
}
}
// Accumulate any SELECT nodes from the right side and add to the left ...
PlanNode topRightSelect = rightChild.findAtOrBelow(Type.SELECT);
if (topRightSelect != null) {
PlanNode bottomRightSelect = topRightSelect;
while (true) {
if (bottomRightSelect.getFirstChild().isNot(Type.SELECT)) break;
bottomRightSelect = bottomRightSelect.getFirstChild();
}
topRightSelect.setParent(null);
bottomRightSelect.removeAllChildren();
// Place just above the left source ...
leftSource.getParent().addLastChild(topRightSelect);
leftSource.setParent(bottomRightSelect);
}
// Now record that references to the right selector name should be removed ...
SelectorName rightTableName = rightSource.getProperty(Property.SOURCE_NAME, SelectorName.class);
SelectorName rightTableAlias = rightSource.getProperty(Property.SOURCE_ALIAS, SelectorName.class);
SelectorName leftTableAlias = leftSource.getProperty(Property.SOURCE_ALIAS, SelectorName.class);
if (leftTableAlias != null) {
if (rightTableName != null) rewrittenSelectors.put(rightTableName, leftTableAlias);
if (rightTableAlias != null) rewrittenSelectors.put(rightTableAlias, leftTableAlias);
} else {
SelectorName leftTableName = leftSource.getProperty(Property.SOURCE_NAME, SelectorName.class);
assert leftTableName != null;
if (rightTableName != null) rewrittenSelectors.put(rightTableName, leftTableName);
if (rightTableAlias != null) rewrittenSelectors.put(rightTableAlias, leftTableName);
}
}
/**
* {@inheritDoc}
*
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return getClass().getSimpleName();
}
}