/*
* 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.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
/**
* A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum
* score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries.
* This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be
* combined equivalently into a single search field). We want the primary score to be the one associated with the highest boost,
* not the sum of the field scores (as BooleanQuery would give).
* If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching
* another gets a higher score than "albino" matching both fields.
* To get this result, use both BooleanQuery and DisjunctionMaxQuery: for each term a DisjunctionMaxQuery searches for it in
* each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery.
* The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that
* include this term in only the best of those multiple fields, without confusing this with the better case of two different terms
* in the multiple fields.
*/
public final class DisjunctionMaxQuery extends Query implements Iterable<Query> {
/* The subqueries */
private final Query[] disjuncts;
/* Multiple of the non-max disjunct scores added into our final score. Non-zero values support tie-breaking. */
private final float tieBreakerMultiplier;
/**
* Creates a new DisjunctionMaxQuery
* @param disjuncts a {@code Collection<Query>} of all the disjuncts to add
* @param tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight
* and added into the final score. If non-zero, the value should be small, on the order of 0.1, which says that
* 10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique
* word in the lower scored field (i.e., one that is not in any higher scored field.
*/
public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier) {
Objects.requireNonNull(disjuncts, "Collection of Querys must not be null");
this.tieBreakerMultiplier = tieBreakerMultiplier;
this.disjuncts = disjuncts.toArray(new Query[disjuncts.size()]);
}
/** @return An {@code Iterator<Query>} over the disjuncts */
@Override
public Iterator<Query> iterator() {
return getDisjuncts().iterator();
}
/**
* @return the disjuncts.
*/
public List<Query> getDisjuncts() {
return Collections.unmodifiableList(Arrays.asList(disjuncts));
}
/**
* @return tie breaker value for multiple matches.
*/
public float getTieBreakerMultiplier() {
return tieBreakerMultiplier;
}
/**
* Expert: the Weight for DisjunctionMaxQuery, used to
* normalize, score and explain these queries.
*
* <p>NOTE: this API and implementation is subject to
* change suddenly in the next release.</p>
*/
protected class DisjunctionMaxWeight extends Weight {
/** The Weights for our subqueries, in 1-1 correspondence with disjuncts */
protected final ArrayList<Weight> weights = new ArrayList<>(); // The Weight's for our subqueries, in 1-1 correspondence with disjuncts
private final boolean needsScores;
/** Construct the Weight for this Query searched by searcher. Recursively construct subquery weights. */
public DisjunctionMaxWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOException {
super(DisjunctionMaxQuery.this);
for (Query disjunctQuery : disjuncts) {
weights.add(searcher.createWeight(disjunctQuery, needsScores, boost));
}
this.needsScores = needsScores;
}
@Override
public void extractTerms(Set<Term> terms) {
for (Weight weight : weights) {
weight.extractTerms(terms);
}
}
/** Create the scorer used to score our associated DisjunctionMaxQuery */
@Override
public Scorer scorer(LeafReaderContext context) throws IOException {
List<Scorer> scorers = new ArrayList<>();
for (Weight w : weights) {
// we will advance() subscorers
Scorer subScorer = w.scorer(context);
if (subScorer != null) {
scorers.add(subScorer);
}
}
if (scorers.isEmpty()) {
// no sub-scorers had any documents
return null;
} else if (scorers.size() == 1) {
// only one sub-scorer in this segment
return scorers.get(0);
} else {
return new DisjunctionMaxScorer(this, tieBreakerMultiplier, scorers, needsScores);
}
}
/** Explain the score we computed for doc */
@Override
public Explanation explain(LeafReaderContext context, int doc) throws IOException {
boolean match = false;
float max = Float.NEGATIVE_INFINITY, sum = 0.0f;
List<Explanation> subs = new ArrayList<>();
for (Weight wt : weights) {
Explanation e = wt.explain(context, doc);
if (e.isMatch()) {
match = true;
subs.add(e);
sum += e.getValue();
max = Math.max(max, e.getValue());
}
}
if (match) {
final float score = max + (sum - max) * tieBreakerMultiplier;
final String desc = tieBreakerMultiplier == 0.0f ? "max of:" : "max plus " + tieBreakerMultiplier + " times others of:";
return Explanation.match(score, desc, subs);
} else {
return Explanation.noMatch("No matching clause");
}
}
} // end of DisjunctionMaxWeight inner class
/** Create the Weight used to score us */
@Override
public Weight createWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOException {
return new DisjunctionMaxWeight(searcher, needsScores, boost);
}
/** Optimize our representation and our subqueries representations
* @param reader the IndexReader we query
* @return an optimized copy of us (which may not be a copy if there is nothing to optimize) */
@Override
public Query rewrite(IndexReader reader) throws IOException {
if (disjuncts.length == 1) {
return disjuncts[0];
}
boolean actuallyRewritten = false;
List<Query> rewrittenDisjuncts = new ArrayList<>();
for (Query sub : disjuncts) {
Query rewrittenSub = sub.rewrite(reader);
actuallyRewritten |= rewrittenSub != sub;
rewrittenDisjuncts.add(rewrittenSub);
}
if (actuallyRewritten) {
return new DisjunctionMaxQuery(rewrittenDisjuncts, tieBreakerMultiplier);
}
return super.rewrite(reader);
}
/** Prettyprint us.
* @param field the field to which we are applied
* @return a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"
*/
@Override
public String toString(String field) {
StringBuilder buffer = new StringBuilder();
buffer.append("(");
for (int i = 0 ; i < disjuncts.length; i++) {
Query subquery = disjuncts[i];
if (subquery instanceof BooleanQuery) { // wrap sub-bools in parens
buffer.append("(");
buffer.append(subquery.toString(field));
buffer.append(")");
}
else buffer.append(subquery.toString(field));
if (i != disjuncts.length-1) buffer.append(" | ");
}
buffer.append(")");
if (tieBreakerMultiplier != 0.0f) {
buffer.append("~");
buffer.append(tieBreakerMultiplier);
}
return buffer.toString();
}
/** Return true iff we represent the same query as o
* @param other another object
* @return true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
*/
@Override
public boolean equals(Object other) {
return sameClassAs(other) &&
equalsTo(getClass().cast(other));
}
private boolean equalsTo(DisjunctionMaxQuery other) {
return tieBreakerMultiplier == other.tieBreakerMultiplier &&
Arrays.equals(disjuncts, other.disjuncts);
}
/** Compute a hash code for hashing us
* @return the hash code
*/
@Override
public int hashCode() {
int h = classHash();
h = 31 * h + Float.floatToIntBits(tieBreakerMultiplier);
h = 31 * h + Arrays.hashCode(disjuncts);
return h;
}
}