org.apache.lucene.search

Class Weight

java.lang.Object

org.apache.lucene.search.Weight

Direct Known Subclasses:

BooleanWeight, ConstantScoreQuery.ConstantWeight, DisjunctionMaxQuery.DisjunctionMaxWeight, SpanWeight

public abstract class Weight
extends Object

Expert: Calculate query weights and build query scorers.

The purpose of Weight is to ensure searching does not modify a Query, so that a Query instance can be reused.
IndexSearcher dependent state of the query should reside in the Weight.
LeafReader dependent state should reside in the Scorer.

Since Weight creates Scorer instances for a given LeafReaderContext (scorer(org.apache.lucene.index.LeafReaderContext, Bits)) callers must maintain the relationship between the searcher's top-level IndexReaderContext and the context used to create a Scorer.

A Weight is used in the following way:

1. A Weight is constructed by a top-level query, given a IndexSearcher (Query.createWeight(IndexSearcher, boolean)).
2. The getValueForNormalization() method is called on the Weight to compute the query normalization factor Similarity.queryNorm(float) of the query clauses contained in the query.
3. The query normalization factor is passed to normalize(float, float). At this point the weighting is complete.
4. A Scorer is constructed by scorer(org.apache.lucene.index.LeafReaderContext, Bits).

Since:

2.9

Field Summary

Fields

Modifier and Type	Field and Description
protected Query	parentQuery

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Weight(Query query) Sole constructor, typically invoked by sub-classes.

Method Summary

Methods

Modifier and Type	Method and Description
BulkScorer	bulkScorer(LeafReaderContext context, Bits acceptDocs) Optional method, to return a BulkScorer to score the query and send hits to a Collector.
abstract Explanation	explain(LeafReaderContext context, int doc) An explanation of the score computation for the named document.
Query	getQuery() The query that this concerns.
abstract float	getValueForNormalization() The value for normalization of contained query clauses (e.g.
abstract void	normalize(float norm, float topLevelBoost) Assigns the query normalization factor and boost from parent queries to this.
abstract Scorer	scorer(LeafReaderContext context, Bits acceptDocs) Returns a Scorer which scores documents in/out-of order according to scoreDocsInOrder.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

parentQuery

protected final Query parentQuery

Constructor Detail

Weight

protected Weight(Query query)

Sole constructor, typically invoked by sub-classes.

Parameters:

query - the parent query

Method Detail

explain

public abstract Explanation explain(LeafReaderContext context,
                  int doc)
                             throws IOException

An explanation of the score computation for the named document.

Parameters:

context - the readers context to create the Explanation for.

doc - the document's id relative to the given context's reader

Returns:

an Explanation for the score

Throws:

IOException - if an IOException occurs

getQuery

public final Query getQuery()

The query that this concerns.

getValueForNormalization

public abstract float getValueForNormalization()
                                        throws IOException

The value for normalization of contained query clauses (e.g. sum of squared weights).

Throws:

IOException

normalize

public abstract void normalize(float norm,
             float topLevelBoost)

Assigns the query normalization factor and boost from parent queries to this.

scorer

public abstract Scorer scorer(LeafReaderContext context,
            Bits acceptDocs)
                       throws IOException

Returns a Scorer which scores documents in/out-of order according to scoreDocsInOrder.

NOTE: null can be returned if no documents will be scored by this query.

Parameters:

context - the LeafReaderContext for which to return the Scorer.

acceptDocs - Bits that represent the allowable docs to match (typically deleted docs but possibly filtering other documents)

Returns:

a Scorer which scores documents in/out-of order.

Throws:

IOException - if there is a low-level I/O error

bulkScorer

public BulkScorer bulkScorer(LeafReaderContext context,
                    Bits acceptDocs)
                      throws IOException

Optional method, to return a BulkScorer to score the query and send hits to a Collector. Only queries that have a different top-level approach need to override this; the default implementation pulls a normal Scorer and iterates and collects the resulting hits.

Parameters:

context - the LeafReaderContext for which to return the Scorer.

acceptDocs - Bits that represent the allowable docs to match (typically deleted docs but possibly filtering other documents)

Returns:

a BulkScorer which scores documents and passes them to a collector.

Throws:

IOException - if there is a low-level I/O error