package org.apache.lucene.search;
/**
* 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.
*/
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.ToStringUtils;
import java.io.IOException;
import java.util.PriorityQueue;
/** Implements the fuzzy search query. The similarity measurement
* is based on the Levenshtein (edit distance) algorithm.
*
* Warning: this query is not very scalable with its default prefix
* length of 0 - in this case, *every* term will be enumerated and
* cause an edit score calculation.
*
*/
public class FuzzyQuery extends MultiTermQuery {
public final static float defaultMinSimilarity = 0.5f;
public final static int defaultPrefixLength = 0;
private float minimumSimilarity;
private int prefixLength;
private boolean termLongEnough = false;
protected Term term;
/**
* Create a new FuzzyQuery that will match terms with a similarity
* of at least <code>minimumSimilarity</code> to <code>term</code>.
* If a <code>prefixLength</code> > 0 is specified, a common prefix
* of that length is also required.
*
* @param term the term to search for
* @param minimumSimilarity a value between 0 and 1 to set the required similarity
* between the query term and the matching terms. For example, for a
* <code>minimumSimilarity</code> of <code>0.5</code> a term of the same length
* as the query term is considered similar to the query term if the edit distance
* between both terms is less than <code>length(term)*0.5</code>
* @param prefixLength length of common (non-fuzzy) prefix
* @throws IllegalArgumentException if minimumSimilarity is >= 1 or < 0
* or if prefixLength < 0
*/
public FuzzyQuery(Term term, float minimumSimilarity, int prefixLength) throws IllegalArgumentException {
this.term = term;
if (minimumSimilarity >= 1.0f)
throw new IllegalArgumentException("minimumSimilarity >= 1");
else if (minimumSimilarity < 0.0f)
throw new IllegalArgumentException("minimumSimilarity < 0");
if (prefixLength < 0)
throw new IllegalArgumentException("prefixLength < 0");
if (term.text().length() > 1.0f / (1.0f - minimumSimilarity)) {
this.termLongEnough = true;
}
this.minimumSimilarity = minimumSimilarity;
this.prefixLength = prefixLength;
rewriteMethod = SCORING_BOOLEAN_QUERY_REWRITE;
}
/**
* Calls {@link #FuzzyQuery(Term, float) FuzzyQuery(term, minimumSimilarity, 0)}.
*/
public FuzzyQuery(Term term, float minimumSimilarity) throws IllegalArgumentException {
this(term, minimumSimilarity, defaultPrefixLength);
}
/**
* Calls {@link #FuzzyQuery(Term, float) FuzzyQuery(term, 0.5f, 0)}.
*/
public FuzzyQuery(Term term) {
this(term, defaultMinSimilarity, defaultPrefixLength);
}
/**
* Returns the minimum similarity that is required for this query to match.
* @return float value between 0.0 and 1.0
*/
public float getMinSimilarity() {
return minimumSimilarity;
}
/**
* Returns the non-fuzzy prefix length. This is the number of characters at the start
* of a term that must be identical (not fuzzy) to the query term if the query
* is to match that term.
*/
public int getPrefixLength() {
return prefixLength;
}
@Override
protected FilteredTermEnum getEnum(IndexReader reader) throws IOException {
return new FuzzyTermEnum(reader, getTerm(), minimumSimilarity, prefixLength);
}
/**
* Returns the pattern term.
*/
public Term getTerm() {
return term;
}
@Override
public void setRewriteMethod(RewriteMethod method) {
throw new UnsupportedOperationException("FuzzyQuery cannot change rewrite method");
}
@Override
public Query rewrite(IndexReader reader) throws IOException {
if(!termLongEnough) { // can only match if it's exact
return new TermQuery(term);
}
int maxSize = BooleanQuery.getMaxClauseCount();
PriorityQueue<ScoreTerm> stQueue = new PriorityQueue<ScoreTerm>();
FilteredTermEnum enumerator = getEnum(reader);
try {
ScoreTerm st = new ScoreTerm();
do {
final Term t = enumerator.term();
if (t == null) break;
final float score = enumerator.difference();
// ignore uncompetetive hits
if (stQueue.size() >= maxSize && score <= stQueue.peek().score)
continue;
// add new entry in PQ
st.term = t;
st.score = score;
stQueue.offer(st);
// possibly drop entries from queue
st = (stQueue.size() > maxSize) ? stQueue.poll() : new ScoreTerm();
} while (enumerator.next());
} finally {
enumerator.close();
}
BooleanQuery query = new BooleanQuery(true);
for (final ScoreTerm st : stQueue) {
TermQuery tq = new TermQuery(st.term); // found a match
tq.setBoost(getBoost() * st.score); // set the boost
query.add(tq, BooleanClause.Occur.SHOULD); // add to query
}
return query;
}
private static final class ScoreTerm implements Comparable<ScoreTerm> {
public Term term;
public float score;
public int compareTo(ScoreTerm other) {
if (this.score == other.score)
return other.term.compareTo(this.term);
else
return Float.compare(this.score, other.score);
}
}
@Override
public String toString(String field) {
final StringBuilder buffer = new StringBuilder();
if (!term.field().equals(field)) {
buffer.append(term.field());
buffer.append(":");
}
buffer.append(term.text());
buffer.append('~');
buffer.append(Float.toString(minimumSimilarity));
buffer.append(ToStringUtils.boost(getBoost()));
return buffer.toString();
}
@Override
public int hashCode() {
final int prime = 31;
int result = super.hashCode();
result = prime * result + Float.floatToIntBits(minimumSimilarity);
result = prime * result + prefixLength;
result = prime * result + ((term == null) ? 0 : term.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (!super.equals(obj))
return false;
if (getClass() != obj.getClass())
return false;
FuzzyQuery other = (FuzzyQuery) obj;
if (Float.floatToIntBits(minimumSimilarity) != Float
.floatToIntBits(other.minimumSimilarity))
return false;
if (prefixLength != other.prefixLength)
return false;
if (term == null) {
if (other.term != null)
return false;
} else if (!term.equals(other.term))
return false;
return true;
}
}