org.apache.lucene.search

Class CombinedFieldQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.CombinedFieldQuery

All Implemented Interfaces:

Accountable

public final class CombinedFieldQuery
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.

The query works as follows:

1. Given a list of fields and weights, it pretends there is a synthetic combined field where all terms have been indexed. It computes new term and collection statistics for this combined field.
2. It uses a disjunction iterator and IndexSearcher.getSimilarity() to score documents.

In order for a similarity to be compatible, Similarity.computeNorm(org.apache.lucene.index.FieldInvertState) must be additive: the norm of the combined field is the sum of norms for each individual field. The norms must also be encoded using SmallFloat.intToByte4(int). These requirements hold for all similarities that compute norms the same way as SimilarityBase.computeNorm(org.apache.lucene.index.FieldInvertState), which includes BM25Similarity and DFRSimilarity. Per-field similarities are not supported.

The query also requires that either all fields or no fields have norms enabled. Having only some fields with norms enabled can result in errors.

The scoring is based on BM25F's simple formula described in: http://www.staff.city.ac.uk/~sb317/papers/foundations_bm25_review.pdf. This query implements the same approach but allows other similarities besides BM25Similarity.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	CombinedFieldQuery.Builder A builder for CombinedFieldQuery.

Field Summary

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

NULL_ACCOUNTABLE

Method Summary

Modifier and Type	Method and Description
Weight	createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
boolean	equals(Object o)
List<Term>	getTerms()
int	hashCode()
long	ramBytesUsed()
Query	rewrite(IndexReader reader)
String	toString(String field)
void	visit(QueryVisitor visitor)

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

Method Detail

getTerms

public List<Term> getTerms()

toString

public String toString(String field)

Specified by:

toString in class Query

equals

public boolean equals(Object o)

Specified by:

equals in class Query

hashCode

public int hashCode()

Specified by:

hashCode in class Query

ramBytesUsed

public long ramBytesUsed()

Specified by:

ramBytesUsed in interface Accountable

rewrite

public Query rewrite(IndexReader reader)
              throws IOException

Overrides:

rewrite in class Query

Throws:

IOException

visit

public void visit(QueryVisitor visitor)

Overrides:

visit in class Query

createWeight

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

Overrides:

createWeight in class Query

Throws:

IOException