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package org.apache.lucene.search;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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import org.apache.lucene.index.IndexReader;
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import org.apache.lucene.index.Term;
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import org.apache.lucene.util.ToStringUtils;
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import java.io.IOException;
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* A query that wraps another query or a filter and simply returns a constant score equal to the
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* query boost for every document that matches the filter or query.
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* For queries it therefore simply strips of all scores and returns a constant one.
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* <p><b>NOTE</b>: if the wrapped filter is an instance of
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* {@link CachingWrapperFilter}, you'll likely want to
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* enforce deletions in the filter (using either {@link
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* CachingWrapperFilter.DeletesMode#RECACHE} or {@link
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* CachingWrapperFilter.DeletesMode#DYNAMIC}).
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public class ConstantScoreQuery extends Query {
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protected final Filter filter;
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protected final Query query;
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/** Strips off scores from the passed in Query. The hits will get a constant score
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* dependent on the boost factor of this query. */
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public ConstantScoreQuery(Query query) {
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throw new NullPointerException("Query may not be null");
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/** Wraps a Filter as a Query. The hits will get a constant score
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* dependent on the boost factor of this query.
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* If you simply want to strip off scores from a Query, no longer use
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* {@code new ConstantScoreQuery(new QueryWrapperFilter(query))}, instead
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* use {@link #ConstantScoreQuery(Query)}!
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public ConstantScoreQuery(Filter filter) {
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throw new NullPointerException("Filter may not be null");
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/** Returns the encapsulated filter, returns {@code null} if a query is wrapped. */
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public Filter getFilter() {
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/** Returns the encapsulated query, returns {@code null} if a filter is wrapped. */
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public Query getQuery() {
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public Query rewrite(IndexReader reader) throws IOException {
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Query rewritten = query.rewrite(reader);
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if (rewritten != query) {
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rewritten = new ConstantScoreQuery(rewritten);
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rewritten.setBoost(this.getBoost());
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public void extractTerms(Set<Term> terms) {
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// TODO: OK to not add any terms when wrapped a filter
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// and used with MultiSearcher, but may not be OK for
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// If a query was wrapped, we delegate to query.
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query.extractTerms(terms);
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protected class ConstantWeight extends Weight {
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private final Weight innerWeight;
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private final Similarity similarity;
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private float queryNorm;
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private float queryWeight;
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public ConstantWeight(Searcher searcher) throws IOException {
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this.similarity = getSimilarity(searcher);
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this.innerWeight = (query == null) ? null : query.createWeight(searcher);
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public Query getQuery() {
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return ConstantScoreQuery.this;
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public float getValue() {
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public float sumOfSquaredWeights() throws IOException {
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// we calculate sumOfSquaredWeights of the inner weight, but ignore it (just to initialize everything)
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if (innerWeight != null) innerWeight.sumOfSquaredWeights();
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queryWeight = getBoost();
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return queryWeight * queryWeight;
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public void normalize(float norm) {
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this.queryNorm = norm;
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queryWeight *= this.queryNorm;
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// we normalize the inner weight, but ignore it (just to initialize everything)
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if (innerWeight != null) innerWeight.normalize(norm);
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public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
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final DocIdSetIterator disi;
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if (filter != null) {
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assert query == null;
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final DocIdSet dis = filter.getDocIdSet(reader);
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disi = dis.iterator();
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assert query != null && innerWeight != null;
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innerWeight.scorer(reader, scoreDocsInOrder, topScorer);
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return new ConstantScorer(similarity, disi, this);
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public boolean scoresDocsOutOfOrder() {
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return (innerWeight != null) ? innerWeight.scoresDocsOutOfOrder() : false;
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public Explanation explain(IndexReader reader, int doc) throws IOException {
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final Scorer cs = scorer(reader, true, false);
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final boolean exists = (cs != null && cs.advance(doc) == doc);
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final ComplexExplanation result = new ComplexExplanation();
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result.setDescription(ConstantScoreQuery.this.toString() + ", product of:");
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result.setValue(queryWeight);
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result.setMatch(Boolean.TRUE);
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result.addDetail(new Explanation(getBoost(), "boost"));
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result.addDetail(new Explanation(queryNorm, "queryNorm"));
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result.setDescription(ConstantScoreQuery.this.toString() + " doesn't match id " + doc);
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result.setMatch(Boolean.FALSE);
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protected class ConstantScorer extends Scorer {
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final DocIdSetIterator docIdSetIterator;
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final float theScore;
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public ConstantScorer(Similarity similarity, DocIdSetIterator docIdSetIterator, Weight w) throws IOException {
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theScore = w.getValue();
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this.docIdSetIterator = docIdSetIterator;
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public int nextDoc() throws IOException {
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return docIdSetIterator.nextDoc();
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return docIdSetIterator.docID();
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public float score() throws IOException {
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public int advance(int target) throws IOException {
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return docIdSetIterator.advance(target);
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private Collector wrapCollector(final Collector collector) {
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return new Collector() {
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public void setScorer(Scorer scorer) throws IOException {
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// we must wrap again here, but using the scorer passed in as parameter:
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collector.setScorer(new ConstantScorer(ConstantScorer.this.getSimilarity(),
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scorer, ConstantScorer.this.weight));
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public void collect(int doc) throws IOException {
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collector.collect(doc);
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public void setNextReader(IndexReader reader, int docBase) throws IOException {
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collector.setNextReader(reader, docBase);
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public boolean acceptsDocsOutOfOrder() {
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return collector.acceptsDocsOutOfOrder();
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// this optimization allows out of order scoring as top scorer!
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public void score(Collector collector) throws IOException {
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if (docIdSetIterator instanceof Scorer) {
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((Scorer) docIdSetIterator).score(wrapCollector(collector));
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super.score(collector);
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// this optimization allows out of order scoring as top scorer,
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// TODO: theoretically this method should not be called because its protected and
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// this class does not use it, it should be public in Scorer!
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protected boolean score(Collector collector, int max, int firstDocID) throws IOException {
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if (docIdSetIterator instanceof Scorer) {
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return ((Scorer) docIdSetIterator).score(wrapCollector(collector), max, firstDocID);
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return super.score(collector, max, firstDocID);
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public Weight createWeight(Searcher searcher) throws IOException {
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return new ConstantScoreQuery.ConstantWeight(searcher);
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public String toString(String field) {
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return new StringBuilder("ConstantScore(")
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.append((query == null) ? filter.toString() : query.toString(field))
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.append(ToStringUtils.boost(getBoost()))
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public boolean equals(Object o) {
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if (this == o) return true;
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if (!super.equals(o))
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if (o instanceof ConstantScoreQuery) {
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final ConstantScoreQuery other = (ConstantScoreQuery) o;
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((this.filter == null) ? other.filter == null : this.filter.equals(other.filter)) &&
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((this.query == null) ? other.query == null : this.query.equals(other.query));
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public int hashCode() {
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return 31 * super.hashCode() +
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((query == null) ? filter : query).hashCode();