Package org.apache.lucene.search

Class Weight

java.lang.Object

org.apache.lucene.search.Weight

Direct Known Subclasses:

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.
AtomicReader dependent state should reside in the Scorer.

Since Weight creates Scorer instances for a given AtomicReaderContext (scorer(AtomicReaderContext, boolean, boolean, 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)).
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(AtomicReaderContext, boolean, boolean, Bits).

Since:

2.9

Constructor Summary

Constructors

Constructor	Description
Weight()

Method Summary

Modifier and Type	Method	Description
abstract Explanation	explain(AtomicReaderContext context, int doc)	An explanation of the score computation for the named document.
abstract 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(AtomicReaderContext context, boolean scoreDocsInOrder, boolean topScorer, Bits acceptDocs)	Returns a Scorer which scores documents in/out-of order according to scoreDocsInOrder.
boolean	scoresDocsOutOfOrder()	Returns true iff this implementation scores docs only out of order.

Methods inherited from class java.lang.Object

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

Constructor Detail

Weight

public Weight()

Method Detail

explain

public abstract Explanation explain(AtomicReaderContext 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 abstract 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(AtomicReaderContext context,
                              boolean scoreDocsInOrder,
                              boolean topScorer,
                              Bits acceptDocs)
                       throws IOException

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

NOTE: even if scoreDocsInOrder is false, it is recommended to check whether the returned Scorer indeed scores documents out of order (i.e., call scoresDocsOutOfOrder()), as some Scorer implementations will always return documents in-order.
NOTE: null can be returned if no documents will be scored by this query.

Parameters:

context - the AtomicReaderContext for which to return the Scorer.

scoreDocsInOrder - specifies whether in-order scoring of documents is required. Note that if set to false (i.e., out-of-order scoring is required), this method can return whatever scoring mode it supports, as every in-order scorer is also an out-of-order one. However, an out-of-order scorer may not support DocIdSetIterator.nextDoc() and/or DocIdSetIterator.advance(int), therefore it is recommended to request an in-order scorer if use of these methods is required.

topScorer - if true, Scorer.score(Collector) will be called; if false, DocIdSetIterator.nextDoc() and/or DocIdSetIterator.advance(int) will be called.

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

scoresDocsOutOfOrder

public boolean scoresDocsOutOfOrder()

Returns true iff this implementation scores docs only out of order. This method is used in conjunction with Collector's acceptsDocsOutOfOrder and scorer(AtomicReaderContext, boolean, boolean, Bits) to create a matching Scorer instance for a given Collector, or vice versa.

NOTE: the default implementation returns false, i.e. the Scorer scores documents in-order.