/*
* 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.Collection;
import java.util.Collections;
/**
* Expert: Common scoring functionality for different types of queries.
*
* <p>
* A <code>Scorer</code> exposes an {@link #iterator()} over documents
* matching a query in increasing order of doc Id.
* </p>
* <p>
* Document scores are computed using a given <code>Similarity</code>
* implementation.
* </p>
*
* <p><b>NOTE</b>: The values Float.Nan,
* Float.NEGATIVE_INFINITY and Float.POSITIVE_INFINITY are
* not valid scores. Certain collectors (eg {@link
* TopScoreDocCollector}) will not properly collect hits
* with these scores.
*/
public abstract class Scorer {
/** the Scorer's parent Weight. in some cases this may be null */
// TODO can we clean this up?
protected final Weight weight;
/**
* Constructs a Scorer
* @param weight The scorers <code>Weight</code>.
*/
protected Scorer(Weight weight) {
this.weight = weight;
}
/**
* Returns the doc ID that is currently being scored.
* This will return {@code -1} if the {@link #iterator()} is not positioned
* or {@link DocIdSetIterator#NO_MORE_DOCS} if it has been entirely consumed.
* @see DocIdSetIterator#docID()
*/
public abstract int docID();
/** Returns the score of the current document matching the query.
* Initially invalid, until {@link DocIdSetIterator#nextDoc()} or
* {@link DocIdSetIterator#advance(int)} is called on the {@link #iterator()}
* the first time, or when called from within {@link LeafCollector#collect}.
*/
public abstract float score() throws IOException;
/** Returns the freq of this Scorer on the current document */
public abstract int freq() throws IOException;
/** returns parent Weight
* @lucene.experimental
*/
public Weight getWeight() {
return weight;
}
/**
* Returns child sub-scorers positioned on the current document
*
* Note that this method should not be called on Scorers passed to {@link LeafCollector#setScorer(Scorer)},
* as these may be synthetic Scorers produced by {@link BulkScorer} which will throw an Exception.
*
* @lucene.experimental
*/
public Collection<ChildScorer> getChildren() throws IOException {
return Collections.emptyList();
}
/** A child Scorer and its relationship to its parent.
* the meaning of the relationship depends upon the parent query.
* @lucene.experimental */
public static class ChildScorer {
/**
* Child Scorer. (note this is typically a direct child, and may
* itself also have children).
*/
public final Scorer child;
/**
* An arbitrary string relating this scorer to the parent.
*/
public final String relationship;
/**
* Creates a new ChildScorer node with the specified relationship.
* <p>
* The relationship can be any be any string that makes sense to
* the parent Scorer.
*/
public ChildScorer(Scorer child, String relationship) {
this.child = child;
this.relationship = relationship;
}
}
/**
* Return a {@link DocIdSetIterator} over matching documents.
*
* The returned iterator will either be positioned on {@code -1} if no
* documents have been scored yet, {@link DocIdSetIterator#NO_MORE_DOCS}
* if all documents have been scored already, or the last document id that
* has been scored otherwise.
*
* The returned iterator is a view: calling this method several times will
* return iterators that have the same state.
*/
public abstract DocIdSetIterator iterator();
/**
* Optional method: Return a {@link TwoPhaseIterator} view of this
* {@link Scorer}. A return value of {@code null} indicates that
* two-phase iteration is not supported.
*
* Note that the returned {@link TwoPhaseIterator}'s
* {@link TwoPhaseIterator#approximation() approximation} must
* advance synchronously with the {@link #iterator()}: advancing the
* approximation must advance the iterator and vice-versa.
*
* Implementing this method is typically useful on {@link Scorer}s
* that have a high per-document overhead in order to confirm matches.
*
* The default implementation returns {@code null}.
*/
public TwoPhaseIterator twoPhaseIterator() {
return null;
}
}