Package 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 they had been indexed in a single field whose values would be the union of the values of the provided fields.

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 don't customize Similarity.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.

This query assumes that all fields share the same analyzer. Scores may not make much sense if all fields don't have the same analyzer.

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	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	Description
Weight	createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)	Expert: Constructs an appropriate Weight implementation for this query.
boolean	equals(Object o)	Override and implement query instance equivalence properly in a subclass.
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(IndexSearcher indexSearcher)	Expert: called to re-write queries into primitive queries.
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

Method Details

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

equals

public boolean equals(Object o)

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 to those of the other instance. Utility methods are provided for certain repetitive code.

Specified by:

equals in class Query

See Also:

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

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)

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(IndexSearcher indexSearcher)
              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.

Callers are expected to call rewrite multiple times if necessary, until the rewritten query is the same as the original query.

The rewrite process may be able to make use of IndexSearcher's executor and be executed in parallel if the executor is provided.

Overrides:

rewrite in class Query

Throws:

IOException

See Also:

• IndexSearcher.rewrite(Query)

visit

public void visit(QueryVisitor visitor)

Description copied from class: Query

Recurse through the query tree, visiting any child queries.

Specified by:

visit in class Query

Parameters:

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

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