org.apache.lucene.search.FuzzyTermsEnum Maven / Gradle / Ivy
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* 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,
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* See the License for the specific language governing permissions and
* limitations under the License.
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package org.apache.lucene.search;
import java.io.IOException;
import java.util.function.Supplier;
import org.apache.lucene.index.ImpactsEnum;
import org.apache.lucene.index.PostingsEnum;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermState;
import org.apache.lucene.index.Terms;
import org.apache.lucene.index.TermsEnum;
import org.apache.lucene.util.Attribute;
import org.apache.lucene.util.AttributeImpl;
import org.apache.lucene.util.AttributeReflector;
import org.apache.lucene.util.AttributeSource;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.UnicodeUtil;
import org.apache.lucene.util.automaton.CompiledAutomaton;
/** Subclass of TermsEnum for enumerating all terms that are similar
* to the specified filter term.
*
* Term enumerations are always ordered by
* {@link BytesRef#compareTo}. Each term in the enumeration is
* greater than all that precede it.
*/
public final class FuzzyTermsEnum extends TermsEnum {
// NOTE: we can't subclass FilteredTermsEnum here because we need to sometimes change actualEnum:
private TermsEnum actualEnum;
private final AttributeSource atts;
// We use this to communicate the score (boost) of the current matched term we are on back to
// MultiTermQuery.TopTermsBlendedFreqScoringRewrite that is collecting the best (default 50) matched terms:
private final BoostAttribute boostAtt;
// MultiTermQuery.TopTermsBlendedFreqScoringRewrite tells us the worst boost still in its queue using this att,
// which we use to know when we can reduce the automaton from ed=2 to ed=1, or ed=0 if only single top term is collected:
private final MaxNonCompetitiveBoostAttribute maxBoostAtt;
private final CompiledAutomaton[] automata;
private final Terms terms;
private final int termLength;
private final Term term;
private float bottom;
private BytesRef bottomTerm;
private BytesRef queuedBottom;
// Maximum number of edits we will accept. This is either 2 or 1 (or, degenerately, 0) passed by the user originally,
// but as we collect terms, we can lower this (e.g. from 2 to 1) if we detect that the term queue is full, and all
// collected terms are ed=1:
private int maxEdits;
/**
* Constructor for enumeration of all terms from specified reader which share a prefix of
* length prefixLength with term and which have at most {@code maxEdits} edits.
*
* After calling the constructor the enumeration is already pointing to the first
* valid term if such a term exists.
*
* @param terms Delivers terms.
* @param term Pattern term.
* @param maxEdits Maximum edit distance.
* @param prefixLength the length of the required common prefix
* @param transpositions whether transpositions should count as a single edit
* @throws IOException if there is a low-level IO error
*/
public FuzzyTermsEnum(Terms terms, Term term, int maxEdits, int prefixLength, boolean transpositions) throws IOException {
this(terms, new AttributeSource(), term, () -> new FuzzyAutomatonBuilder(term.text(), maxEdits, prefixLength, transpositions));
}
/**
* Constructor for enumeration of all terms from specified reader which share a prefix of
* length prefixLength with term and which have at most {@code maxEdits} edits.
*
* After calling the constructor the enumeration is already pointing to the first
* valid term if such a term exists.
*
* @param terms Delivers terms.
* @param atts An AttributeSource used to share automata between segments
* @param term Pattern term.
* @param maxEdits Maximum edit distance.
* @param prefixLength the length of the required common prefix
* @param transpositions whether transpositions should count as a single edit
* @throws IOException if there is a low-level IO error
*/
FuzzyTermsEnum(Terms terms, AttributeSource atts, Term term, int maxEdits, int prefixLength, boolean transpositions) throws IOException {
this(terms, atts, term, () -> new FuzzyAutomatonBuilder(term.text(), maxEdits, prefixLength, transpositions));
}
private FuzzyTermsEnum(Terms terms, AttributeSource atts, Term term, Supplier automatonBuilder) throws IOException {
this.terms = terms;
this.atts = atts;
this.term = term;
this.maxBoostAtt = atts.addAttribute(MaxNonCompetitiveBoostAttribute.class);
this.boostAtt = atts.addAttribute(BoostAttribute.class);
atts.addAttributeImpl(new AutomatonAttributeImpl());
AutomatonAttribute aa = atts.addAttribute(AutomatonAttribute.class);
aa.init(automatonBuilder);
this.automata = aa.getAutomata();
this.termLength = aa.getTermLength();
this.maxEdits = this.automata.length - 1;
bottom = maxBoostAtt.getMaxNonCompetitiveBoost();
bottomTerm = maxBoostAtt.getCompetitiveTerm();
bottomChanged(null);
}
/**
* Sets the maximum non-competitive boost, which may allow switching to a
* lower max-edit automaton at run time
*/
public void setMaxNonCompetitiveBoost(float boost) {
this.maxBoostAtt.setMaxNonCompetitiveBoost(boost);
}
/**
* Gets the boost of the current term
*/
public float getBoost() {
return boostAtt.getBoost();
}
/**
* return an automata-based enum for matching up to editDistance from
* lastTerm, if possible
*/
private TermsEnum getAutomatonEnum(int editDistance, BytesRef lastTerm) throws IOException {
assert editDistance < automata.length;
final CompiledAutomaton compiled = automata[editDistance];
BytesRef initialSeekTerm;
if (lastTerm == null) {
// This is the first enum we are pulling:
initialSeekTerm = null;
} else {
// We are pulling this enum (e.g., ed=1) after iterating for a while already (e.g., ed=2):
initialSeekTerm = compiled.floor(lastTerm, new BytesRefBuilder());
}
return terms.intersect(compiled, initialSeekTerm);
}
/**
* fired when the max non-competitive boost has changed. this is the hook to
* swap in a smarter actualEnum.
*/
private void bottomChanged(BytesRef lastTerm) throws IOException {
int oldMaxEdits = maxEdits;
// true if the last term encountered is lexicographically equal or after the bottom term in the PQ
boolean termAfter = bottomTerm == null || (lastTerm != null && lastTerm.compareTo(bottomTerm) >= 0);
// as long as the max non-competitive boost is >= the max boost
// for some edit distance, keep dropping the max edit distance.
while (maxEdits > 0) {
float maxBoost = 1.0f - ((float) maxEdits / (float) termLength);
if (bottom < maxBoost || (bottom == maxBoost && termAfter == false)) {
break;
}
maxEdits--;
}
if (oldMaxEdits != maxEdits || lastTerm == null) {
// This is a very powerful optimization: the maximum edit distance has changed. This happens because we collect only the top scoring
// N (= 50, by default) terms, and if e.g. maxEdits=2, and the queue is now full of matching terms, and we notice that the worst entry
// in that queue is ed=1, then we can switch the automata here to ed=1 which is a big speedup.
actualEnum = getAutomatonEnum(maxEdits, lastTerm);
}
}
@Override
public BytesRef next() throws IOException {
if (queuedBottom != null) {
bottomChanged(queuedBottom);
queuedBottom = null;
}
BytesRef term;
term = actualEnum.next();
if (term == null) {
// end
return null;
}
int ed = maxEdits;
// we know the outer DFA always matches.
// now compute exact edit distance
while (ed > 0) {
if (matches(term, ed - 1)) {
ed--;
} else {
break;
}
}
if (ed == 0) { // exact match
boostAtt.setBoost(1.0F);
} else {
final int codePointCount = UnicodeUtil.codePointCount(term);
int minTermLength = Math.min(codePointCount, termLength);
float similarity = 1.0f - (float) ed / (float) minTermLength;
boostAtt.setBoost(similarity);
}
final float bottom = maxBoostAtt.getMaxNonCompetitiveBoost();
final BytesRef bottomTerm = maxBoostAtt.getCompetitiveTerm();
if (bottom != this.bottom || bottomTerm != this.bottomTerm) {
this.bottom = bottom;
this.bottomTerm = bottomTerm;
// clone the term before potentially doing something with it
// this is a rare but wonderful occurrence anyway
// We must delay bottomChanged until the next next() call otherwise we mess up docFreq(), etc., for the current term:
queuedBottom = BytesRef.deepCopyOf(term);
}
return term;
}
/** returns true if term is within k edits of the query term */
private boolean matches(BytesRef termIn, int k) {
return k == 0 ? termIn.equals(term.bytes()) : automata[k].runAutomaton.run(termIn.bytes, termIn.offset, termIn.length);
}
// proxy all other enum calls to the actual enum
@Override
public int docFreq() throws IOException {
return actualEnum.docFreq();
}
@Override
public long totalTermFreq() throws IOException {
return actualEnum.totalTermFreq();
}
@Override
public PostingsEnum postings(PostingsEnum reuse, int flags) throws IOException {
return actualEnum.postings(reuse, flags);
}
@Override
public ImpactsEnum impacts(int flags) throws IOException {
return actualEnum.impacts(flags);
}
@Override
public void seekExact(BytesRef term, TermState state) throws IOException {
actualEnum.seekExact(term, state);
}
@Override
public TermState termState() throws IOException {
return actualEnum.termState();
}
@Override
public long ord() throws IOException {
return actualEnum.ord();
}
@Override
public AttributeSource attributes() {
return atts;
}
@Override
public boolean seekExact(BytesRef text) throws IOException {
return actualEnum.seekExact(text);
}
@Override
public SeekStatus seekCeil(BytesRef text) throws IOException {
return actualEnum.seekCeil(text);
}
@Override
public void seekExact(long ord) throws IOException {
actualEnum.seekExact(ord);
}
@Override
public BytesRef term() throws IOException {
return actualEnum.term();
}
/**
* Thrown to indicate that there was an issue creating a fuzzy query for a given term.
* Typically occurs with terms longer than 220 UTF-8 characters,
* but also possible with shorter terms consisting of UTF-32 code points.
*/
public static class FuzzyTermsException extends RuntimeException {
FuzzyTermsException(String term, Throwable cause) {
super("Term too complex: " + term, cause);
}
}
/**
* Used for sharing automata between segments
*
* Levenshtein automata are large and expensive to build; we don't want to build
* them directly on the query because this can blow up caches that use queries
* as keys; we also don't want to rebuild them for every segment. This attribute
* allows the FuzzyTermsEnum to build the automata once for its first segment
* and then share them for subsequent segment calls.
*/
private interface AutomatonAttribute extends Attribute {
CompiledAutomaton[] getAutomata();
int getTermLength();
void init(Supplier builder);
}
private static class AutomatonAttributeImpl extends AttributeImpl implements AutomatonAttribute {
private CompiledAutomaton[] automata;
private int termLength;
@Override
public CompiledAutomaton[] getAutomata() {
return automata;
}
@Override
public int getTermLength() {
return termLength;
}
@Override
public void init(Supplier supplier) {
if (automata != null) {
return;
}
FuzzyAutomatonBuilder builder = supplier.get();
this.termLength = builder.getTermLength();
this.automata = builder.buildAutomatonSet();
}
@Override
public void clear() {
this.automata = null;
}
@Override
public void reflectWith(AttributeReflector reflector) {
throw new UnsupportedOperationException();
}
@Override
public void copyTo(AttributeImpl target) {
throw new UnsupportedOperationException();
}
}
}