Package org.apache.lucene.search

Class BM25FQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.BM25FQuery

All Implemented Interfaces:

Accountable

public final class BM25FQuery
extends Query
implements Accountable

A Query that treats multiple fields as a single stream and scores terms as if you had indexed them as a single term in a single field. For scoring purposes this query implements the BM25F's simple formula described in: http://www.staff.city.ac.uk/~sb317/papers/foundations_bm25_review.pdf The per-field similarity is ignored but to be compatible each field must use a Similarity at index time that encodes norms the same way as SimilarityBase.computeNorm(org.apache.lucene.index.FieldInvertState).

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private static class	BM25FQuery.BM25FScorer
(package private) class	BM25FQuery.BM25FWeight
static class	BM25FQuery.Builder	A builder for BM25FQuery.
(package private) static class	BM25FQuery.FieldAndWeight
private static class	BM25FQuery.WeightedDisiWrapper

Field Summary

Fields

Modifier and Type	Field	Description
private static final long	BASE_RAM_BYTES
private final TreeMap<String,BM25FQuery.FieldAndWeight>	fieldAndWeights
private final Term[]	fieldTerms
private final long	ramBytesUsed
private final BM25Similarity	similarity
private final BytesRef[]	terms

Fields inherited from interface org.apache.lucene.util.Accountable

NULL_ACCOUNTABLE

Constructor Summary

Constructors

Modifier	Constructor	Description
private	BM25FQuery(BM25Similarity similarity, TreeMap<String,BM25FQuery.FieldAndWeight> fieldAndWeights, BytesRef[] terms)

Method Summary

Modifier and Type	Method	Description
Weight	createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)	Expert: Constructs an appropriate Weight implementation for this query.
boolean	equals(Object other)	Override and implement query instance equivalence properly in a subclass.
List<Term>	getTerms()
int	hashCode()	Override and implement query hash code properly in a subclass.
long	ramBytesUsed()	Return the memory usage of this object in bytes.
Query	rewrite(IndexReader reader)	Expert: called to re-write queries into primitive queries.
private BooleanQuery	rewriteToBoolean()
String	toString(String field)	Prints a query to a string, with field assumed to be the default field and omitted.
void	visit(QueryVisitor visitor)	Recurse through the query tree, visiting any child queries

Methods inherited from class org.apache.lucene.search.Query

classHash, sameClassAs, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.lucene.util.Accountable

getChildResources

Field Details

BASE_RAM_BYTES

private static final long BASE_RAM_BYTES

similarity

private final BM25Similarity similarity

fieldAndWeights

private final TreeMap<String,BM25FQuery.FieldAndWeight> fieldAndWeights

terms

private final BytesRef[] terms

fieldTerms

private final Term[] fieldTerms

ramBytesUsed

private final long ramBytesUsed

Constructor Details

BM25FQuery

private BM25FQuery(BM25Similarity similarity,
 TreeMap<String,BM25FQuery.FieldAndWeight> fieldAndWeights,
 BytesRef[] terms)

Method Details

getTerms

public List<Term> getTerms()

toString

public String toString(String field)

Description copied from class: Query

Prints a query to a string, with field assumed to be the default field and omitted.

Specified by:

toString in class Query

hashCode

public int hashCode()

Description copied from class: Query

Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.

Specified by:

hashCode in class Query

See Also:

• Query.equals(Object)

equals

public boolean equals(Object other)

Description copied from class: Query

Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly. Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.

Specified by:

equals in class Query

See Also:

• Query.sameClassAs(Object)
• Query.classHash()

ramBytesUsed

public long ramBytesUsed()

Description copied from interface: Accountable

Return the memory usage of this object in bytes. Negative values are illegal.

Specified by:

ramBytesUsed in interface Accountable

rewrite

public Query rewrite(IndexReader reader)
              throws IOException

Description copied from class: Query

Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

Overrides:

rewrite in class Query

Throws:

IOException

visit

public void visit(QueryVisitor visitor)

Description copied from class: Query

Recurse through the query tree, visiting any child queries

Overrides:

visit in class Query

Parameters:

visitor - a QueryVisitor to be called by each query in the tree

rewriteToBoolean

private BooleanQuery rewriteToBoolean()

createWeight

public Weight createWeight(IndexSearcher searcher,
 ScoreMode scoreMode,
 float boost)
                    throws IOException

Description copied from class: Query

Expert: Constructs an appropriate Weight implementation for this query.

Only implemented by primitive queries, which re-write to themselves.

Overrides:

createWeight in class Query

Parameters:

scoreMode - How the produced scorers will be consumed.

boost - The boost that is propagated by the parent queries.

Throws:

IOException