Class Weight

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 (GetScorer(AtomicReaderContext, IBits)) 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 (CreateWeight(IndexSearcher)).
  2. The GetValueForNormalization() method is called on the Weight to compute the query normalization factor QueryNorm(Single) of the query clauses contained in the query.
  3. The query normalization factor is passed to Normalize(Single, Single). At this point the weighting is complete.
  4. A Scorer is constructed by GetScorer(AtomicReaderContext, IBits).

@since 2.9

Inheritance
System.Object
Weight
BooleanQuery.BooleanWeight
ConstantScoreQuery.ConstantWeight
DisjunctionMaxQuery.DisjunctionMaxWeight
SpanWeight
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: Lucene.Net.Search
Assembly: Lucene.Net.dll
Syntax
public abstract class Weight

Properties

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Query

The query that this concerns.

Declaration
public abstract Query Query { get; }
Property Value
Type Description
Query
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ScoresDocsOutOfOrder

Returns true if this implementation scores docs only out of order. This method is used in conjunction with ICollector's AcceptsDocsOutOfOrder and GetBulkScorer(AtomicReaderContext, Boolean, IBits) to create a matching Scorer instance for a given ICollector, or vice versa.

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

Declaration
public virtual bool ScoresDocsOutOfOrder { get; }
Property Value
Type Description
System.Boolean

Methods

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Explain(AtomicReaderContext, Int32)

An explanation of the score computation for the named document.

Declaration
public abstract Explanation Explain(AtomicReaderContext context, int doc)
Parameters
Type Name Description
AtomicReaderContext context

The readers context to create the Explanation for.

System.Int32 doc

The document's id relative to the given context's reader

Returns
Type Description
Explanation

An Explanation for the score

Exceptions
Type Condition
System.IO.IOException

if an System.IO.IOException occurs

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GetBulkScorer(AtomicReaderContext, Boolean, IBits)

Optional method, to return a BulkScorer to score the query and send hits to a ICollector. 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.

Declaration
public virtual BulkScorer GetBulkScorer(AtomicReaderContext context, bool scoreDocsInOrder, IBits acceptDocs)
Parameters
Type Name Description
AtomicReaderContext context

The AtomicReaderContext for which to return the Scorer.

System.Boolean 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 NextDoc() and/or Advance(Int32), therefore it is recommended to request an in-order scorer if use of these methods is required.

IBits acceptDocs

IBits that represent the allowable docs to match (typically deleted docs but possibly filtering other documents)
Returns
Type Description
BulkScorer

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

Exceptions
Type Condition
System.IO.IOException

if there is a low-level I/O error

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GetScorer(AtomicReaderContext, IBits)

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.

Declaration
public abstract Scorer GetScorer(AtomicReaderContext context, IBits acceptDocs)
Parameters
Type Name Description
AtomicReaderContext context

The AtomicReaderContext for which to return the Scorer.

IBits acceptDocs

IBits that represent the allowable docs to match (typically deleted docs but possibly filtering other documents)
Returns
Type Description
Scorer

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

Exceptions
Type Condition
System.IO.IOException

if there is a low-level I/O error

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GetValueForNormalization()

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

Declaration
public abstract float GetValueForNormalization()
Returns
Type Description
System.Single
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Normalize(Single, Single)

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

Declaration
public abstract void Normalize(float norm, float topLevelBoost)
Parameters
Type Name Description
System.Single norm
System.Single topLevelBoost