/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.lucene.search;
import java.io.IOException;
import java.util.Set;
import org.apache.lucene.index.IndexReaderContext;
import org.apache.lucene.index.LeafReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.Bits;
/**
* Expert: Calculate query weights and build query scorers.
* <p>
* The purpose of {@link Weight} is to ensure searching does not modify a
* {@link Query}, so that a {@link Query} instance can be reused. <br>
* {@link IndexSearcher} dependent state of the query should reside in the
* {@link Weight}. <br>
* {@link org.apache.lucene.index.LeafReader} dependent state should reside in the {@link Scorer}.
* <p>
* Since {@link Weight} creates {@link Scorer} instances for a given
* {@link org.apache.lucene.index.LeafReaderContext} ({@link #scorer(org.apache.lucene.index.LeafReaderContext)})
* callers must maintain the relationship between the searcher's top-level
* {@link IndexReaderContext} and the context used to create a {@link Scorer}.
* <p>
* A <code>Weight</code> is used in the following way:
* <ol>
* <li>A <code>Weight</code> is constructed by a top-level query, given a
* <code>IndexSearcher</code> ({@link Query#createWeight(IndexSearcher, boolean, float)}).
* <li>A <code>Scorer</code> is constructed by
* {@link #scorer(org.apache.lucene.index.LeafReaderContext)}.
* </ol>
*
* @since 2.9
*/
public abstract class Weight {
protected final Query parentQuery;
/** Sole constructor, typically invoked by sub-classes.
* @param query the parent query
*/
protected Weight(Query query) {
this.parentQuery = query;
}
/**
* Expert: adds all terms occurring in this query to the terms set. If the
* {@link Weight} was created with {@code needsScores == true} then this
* method will only extract terms which are used for scoring, otherwise it
* will extract all terms which are used for matching.
*/
public abstract void extractTerms(Set<Term> terms);
/**
* An explanation of the score computation for the named document.
*
* @param context the readers context to create the {@link Explanation} for.
* @param doc the document's id relative to the given context's reader
* @return an Explanation for the score
* @throws IOException if an {@link IOException} occurs
*/
public abstract Explanation explain(LeafReaderContext context, int doc) throws IOException;
/** The query that this concerns. */
public final Query getQuery() {
return parentQuery;
}
/**
* Returns a {@link Scorer} which can iterate in order over all matching
* documents and assign them a score.
* <p>
* <b>NOTE:</b> null can be returned if no documents will be scored by this
* query.
* <p>
* <b>NOTE</b>: The returned {@link Scorer} does not have
* {@link LeafReader#getLiveDocs()} applied, they need to be checked on top.
*
* @param context
* the {@link org.apache.lucene.index.LeafReaderContext} for which to return the {@link Scorer}.
*
* @return a {@link Scorer} which scores documents in/out-of order.
* @throws IOException if there is a low-level I/O error
*/
public abstract Scorer scorer(LeafReaderContext context) throws IOException;
/**
* Optional method.
* Get a {@link ScorerSupplier}, which allows to know the cost of the {@link Scorer}
* before building it. The default implementation calls {@link #scorer} and
* builds a {@link ScorerSupplier} wrapper around it.
* @see #scorer
*/
public ScorerSupplier scorerSupplier(LeafReaderContext context) throws IOException {
final Scorer scorer = scorer(context);
if (scorer == null) {
return null;
}
return new ScorerSupplier() {
@Override
public Scorer get(boolean randomAccess) {
return scorer;
}
@Override
public long cost() {
return scorer.iterator().cost();
}
};
}
/**
* Optional method, to return a {@link BulkScorer} to
* score the query and send hits to a {@link Collector}.
* Only queries that have a different top-level approach
* need to override this; the default implementation
* pulls a normal {@link Scorer} and iterates and
* collects the resulting hits which are not marked as deleted.
*
* @param context
* the {@link org.apache.lucene.index.LeafReaderContext} for which to return the {@link Scorer}.
*
* @return a {@link BulkScorer} which scores documents and
* passes them to a collector.
* @throws IOException if there is a low-level I/O error
*/
public BulkScorer bulkScorer(LeafReaderContext context) throws IOException {
Scorer scorer = scorer(context);
if (scorer == null) {
// No docs match
return null;
}
// This impl always scores docs in order, so we can
// ignore scoreDocsInOrder:
return new DefaultBulkScorer(scorer);
}
/** Just wraps a Scorer and performs top scoring using it.
* @lucene.internal */
protected static class DefaultBulkScorer extends BulkScorer {
private final Scorer scorer;
private final DocIdSetIterator iterator;
private final TwoPhaseIterator twoPhase;
/** Sole constructor. */
public DefaultBulkScorer(Scorer scorer) {
if (scorer == null) {
throw new NullPointerException();
}
this.scorer = scorer;
this.iterator = scorer.iterator();
this.twoPhase = scorer.twoPhaseIterator();
}
@Override
public long cost() {
return iterator.cost();
}
@Override
public int score(LeafCollector collector, Bits acceptDocs, int min, int max) throws IOException {
collector.setScorer(scorer);
if (scorer.docID() == -1 && min == 0 && max == DocIdSetIterator.NO_MORE_DOCS) {
scoreAll(collector, iterator, twoPhase, acceptDocs);
return DocIdSetIterator.NO_MORE_DOCS;
} else {
int doc = scorer.docID();
if (doc < min) {
if (twoPhase == null) {
doc = iterator.advance(min);
} else {
doc = twoPhase.approximation().advance(min);
}
}
return scoreRange(collector, iterator, twoPhase, acceptDocs, doc, max);
}
}
/** Specialized method to bulk-score a range of hits; we
* separate this from {@link #scoreAll} to help out
* hotspot.
* See <a href="https://issues.apache.org/jira/browse/LUCENE-5487">LUCENE-5487</a> */
static int scoreRange(LeafCollector collector, DocIdSetIterator iterator, TwoPhaseIterator twoPhase,
Bits acceptDocs, int currentDoc, int end) throws IOException {
if (twoPhase == null) {
while (currentDoc < end) {
if (acceptDocs == null || acceptDocs.get(currentDoc)) {
collector.collect(currentDoc);
}
currentDoc = iterator.nextDoc();
}
return currentDoc;
} else {
final DocIdSetIterator approximation = twoPhase.approximation();
while (currentDoc < end) {
if ((acceptDocs == null || acceptDocs.get(currentDoc)) && twoPhase.matches()) {
collector.collect(currentDoc);
}
currentDoc = approximation.nextDoc();
}
return currentDoc;
}
}
/** Specialized method to bulk-score all hits; we
* separate this from {@link #scoreRange} to help out
* hotspot.
* See <a href="https://issues.apache.org/jira/browse/LUCENE-5487">LUCENE-5487</a> */
static void scoreAll(LeafCollector collector, DocIdSetIterator iterator, TwoPhaseIterator twoPhase, Bits acceptDocs) throws IOException {
if (twoPhase == null) {
for (int doc = iterator.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = iterator.nextDoc()) {
if (acceptDocs == null || acceptDocs.get(doc)) {
collector.collect(doc);
}
}
} else {
// The scorer has an approximation, so run the approximation first, then check acceptDocs, then confirm
final DocIdSetIterator approximation = twoPhase.approximation();
for (int doc = approximation.nextDoc(); doc != DocIdSetIterator.NO_MORE_DOCS; doc = approximation.nextDoc()) {
if ((acceptDocs == null || acceptDocs.get(doc)) && twoPhase.matches()) {
collector.collect(doc);
}
}
}
}
}
}