org.modeshape.jcr.query.process.NestedLoopJoinComponent Maven / Gradle / Ivy
/*
* ModeShape (http://www.modeshape.org)
* 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.
*
* ModeShape is free software. Unless otherwise indicated, all code in ModeShape
* 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.
*
* ModeShape 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.modeshape.jcr.query.process;
import java.util.ArrayList;
import java.util.List;
import org.modeshape.jcr.query.QueryContext;
import org.modeshape.jcr.query.model.JoinCondition;
import org.modeshape.jcr.query.model.JoinType;
/**
*
*/
public class NestedLoopJoinComponent extends JoinComponent {
public NestedLoopJoinComponent( QueryContext context,
ProcessingComponent left,
ProcessingComponent right,
JoinCondition condition,
JoinType joinType ) {
super(context, left, right, condition, joinType);
}
@Override
public List execute() {
// Construct the necessary components ...
final ValueSelector leftSelector = valueSelectorFor(left(), getJoinCondition());
final ValueSelector rightSelector = valueSelectorFor(right(), getJoinCondition());
final Joinable joinable = joinableFor(left(), right(), getJoinCondition());
final JoinType joinType = getJoinType();
final TupleMerger merger = createMerger(getColumns(), left().getColumns(), right().getColumns());
// Walk through the left and right results ...
List leftTuples = left().execute();
List rightTuples = right().execute();
List tuples = null;
switch (joinType) {
case INNER:
// Note that in SQL joins, a NULL value on one side of the join criteria is not considered equal to
// a NULL value on the other side. Therefore, in the following algorithms, we're shortcutting the
// loops as soon as we get any NULL value for the join criteria.
// see http://en.wikipedia.org/wiki/Join_(SQL)#Inner_join
// Must match tuples on left with those on right, so we'll have no more result tuples than the
// minumum number of tuples on the left or right...
int maxSize = Math.min(leftTuples.size(), rightTuples.size());
tuples = new ArrayList(maxSize);
// Iterate through all the tuples on the left ...
for (Object[] leftTuple : leftTuples) {
Object leftValue = leftSelector.evaluate(leftTuple);
if (leftValue == null) {
continue;
}
// And then find the matching ones on the right ...
for (Object[] rightTuple : rightTuples) {
// Get the value from the left and right side ...
Object rightValue = rightSelector.evaluate(rightTuple);
if (rightValue == null) {
continue;
}
// Determine if the tuples should be joined ...
if (joinable.evaluate(leftValue, rightValue)) {
Object[] result = merger.merge(leftTuple, rightTuple);
tuples.add(result);
}
}
}
break;
case LEFT_OUTER:
// We'll have all the tuples on the left, with any of those on the right that match ...
maxSize = leftTuples.size();
tuples = new ArrayList(maxSize);
// Iterate through all the tuples on the left ...
for (Object[] leftTuple : leftTuples) {
Object leftValue = leftSelector.evaluate(leftTuple);
// And then find the matching ones on the right ...
boolean foundMatch = false;
if (leftValue != null) {
for (Object[] rightTuple : rightTuples) {
// Get the value from the left and right side ...
Object rightValue = rightSelector.evaluate(rightTuple);
if (rightValue == null) {
continue;
}
// Determine if the tuples should be joined ...
if (joinable.evaluate(leftValue, rightValue)) {
Object[] result = merger.merge(leftTuple, rightTuple);
tuples.add(result);
foundMatch = true;
}
}
}
// We've processed all the tuples on the right, and if we've not yet found a match
// we still need to include the left tuple (but we only want to include it once) ...
if (!foundMatch) {
tuples.add(merger.merge(leftTuple, null));
}
}
break;
case RIGHT_OUTER:
// We'll have all the tuples on the right, with any of those on the left that match ...
maxSize = rightTuples.size();
tuples = new ArrayList(maxSize);
// Iterate through all the tuples on the right ...
for (Object[] rightTuple : rightTuples) {
Object rightValue = rightSelector.evaluate(rightTuple);
// And then find the matching ones on the right ...
boolean foundMatch = false;
if (rightValue != null) {
for (Object[] leftTuple : leftTuples) {
// Get the value from the left and right side ...
Object leftValue = leftSelector.evaluate(leftTuple);
if (leftValue == null) {
continue;
}
// Determine if the tuples should be joined ...
if (joinable.evaluate(leftValue, rightValue)) {
Object[] result = merger.merge(leftTuple, rightTuple);
tuples.add(result);
foundMatch = true;
}
}
}
// We've processed all the tuples on the left, and if we've not yet found a match
// we still need to include the right tuple (but we only want to include it once) ...
if (!foundMatch) {
tuples.add(merger.merge(null, rightTuple));
}
}
break;
case FULL_OUTER:
// We'll have all the tuples on the right and all the tuples on the left, and in the worst case
// none will match, so we'll start with the sum of the number of tuples on the left plus the number
// on the right ...
maxSize = leftTuples.size() + rightTuples.size();
tuples = new ArrayList(maxSize);
// Iterate through all the tuples on the left ...
for (Object[] leftTuple : leftTuples) {
Object leftValue = leftSelector.evaluate(leftTuple);
// And then find the matching ones on the right ...
boolean foundMatch = false;
for (Object[] rightTuple : rightTuples) {
// Get the value from the left and right side ...
Object rightValue = rightSelector.evaluate(rightTuple);
if (rightValue == null) continue;
// Determine if the tuples should be joined ...
if (joinable.evaluate(leftValue, rightValue)) {
Object[] result = merger.merge(leftTuple, rightTuple);
tuples.add(result);
foundMatch = true;
} else {
// Otherwise, we still return the right tuple ...
tuples.add(merger.merge(null, rightTuple));
}
}
// We've processed all the tuples on the right, and if we've not yet found a match
// we still need to include the left tuple (but we only want to include it once) ...
if (!foundMatch) {
tuples.add(merger.merge(leftTuple, null));
}
}
break;
case CROSS:
// A cross join results in the Cartesian product, so each tuple on the left will be combined with
// each tuple on the right ...
maxSize = leftTuples.size() * rightTuples.size();
tuples = new ArrayList(maxSize);
// Iterate through all the tuples on the left ...
for (Object[] leftTuple : leftTuples) {
// And for each iterate through all the tuples on the left ...
for (Object[] rightTuple : rightTuples) {
// We always use both tuples ...
Object[] result = merger.merge(leftTuple, rightTuple);
tuples.add(result);
}
}
break;
}
assert tuples != null;
return tuples;
}
}
© 2015 - 2025 Weber Informatics LLC | Privacy Policy