Package org.apache.lucene.search

Class MultiTermQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.MultiTermQuery

Direct Known Subclasses:

AutomatonQuery, FuzzyQuery, TermInSetQuery

public abstract class MultiTermQuery
extends Query

An abstract Query that matches documents containing a subset of terms provided by a FilteredTermsEnum enumeration.

This query cannot be used directly; you must subclass it and define getTermsEnum(Terms,AttributeSource) to provide a FilteredTermsEnum that iterates through the terms to be matched.

NOTE: if MultiTermQuery.RewriteMethod is either CONSTANT_SCORE_BOOLEAN_REWRITE or SCORING_BOOLEAN_REWRITE, you may encounter a IndexSearcher.TooManyClauses exception during searching, which happens when the number of terms to be searched exceeds IndexSearcher.getMaxClauseCount(). Setting MultiTermQuery.RewriteMethod to CONSTANT_SCORE_BLENDED_REWRITE or CONSTANT_SCORE_REWRITE prevents this.

The recommended rewrite method is CONSTANT_SCORE_BLENDED_REWRITE: it doesn't spend CPU computing unhelpful scores, and is the most performant rewrite method given the query. If you need scoring (like FuzzyQuery, use MultiTermQuery.TopTermsScoringBooleanQueryRewrite which uses a priority queue to only collect competitive terms and not hit this limitation.

Note that org.apache.lucene.queryparser.classic.QueryParser produces MultiTermQueries using CONSTANT_SCORE_REWRITE by default.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	MultiTermQuery.RewriteMethod	Abstract class that defines how the query is rewritten.
static class	MultiTermQuery.TopTermsBlendedFreqScoringRewrite	A rewrite method that first translates each term into BooleanClause.Occur.SHOULD clause in a BooleanQuery, but adjusts the frequencies used for scoring to be blended across the terms, otherwise the rarest term typically ranks highest (often not useful eg in the set of expanded terms in a FuzzyQuery).
static class	MultiTermQuery.TopTermsBoostOnlyBooleanQueryRewrite	A rewrite method that first translates each term into BooleanClause.Occur.SHOULD clause in a BooleanQuery, but the scores are only computed as the boost.
static class	MultiTermQuery.TopTermsScoringBooleanQueryRewrite	A rewrite method that first translates each term into BooleanClause.Occur.SHOULD clause in a BooleanQuery, and keeps the scores as computed by the query.

Field Summary

Fields

Modifier and Type	Field	Description
static MultiTermQuery.RewriteMethod	CONSTANT_SCORE_BLENDED_REWRITE	A rewrite method where documents are assigned a constant score equal to the query's boost.
static MultiTermQuery.RewriteMethod	CONSTANT_SCORE_BOOLEAN_REWRITE	Like SCORING_BOOLEAN_REWRITE except scores are not computed.
static MultiTermQuery.RewriteMethod	CONSTANT_SCORE_REWRITE	A rewrite method that first creates a private Filter, by visiting each term in sequence and marking all docs for that term.
static MultiTermQuery.RewriteMethod	DOC_VALUES_REWRITE	A rewrite method that uses DocValuesType.SORTED / DocValuesType.SORTED_SET doc values to find matching docs through a post-filtering type approach.
protected String	field
protected MultiTermQuery.RewriteMethod	rewriteMethod
static MultiTermQuery.RewriteMethod	SCORING_BOOLEAN_REWRITE	A rewrite method that first translates each term into BooleanClause.Occur.SHOULD clause in a BooleanQuery, and keeps the scores as computed by the query.

Constructor Summary

Constructors

Constructor	Description
MultiTermQuery(String field, MultiTermQuery.RewriteMethod rewriteMethod)	Constructs a query matching terms that cannot be represented with a single Term.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object other)	Override and implement query instance equivalence properly in a subclass.
String	getField()	Returns the field name for this query
MultiTermQuery.RewriteMethod	getRewriteMethod()
long	getTermsCount()	Return the number of unique terms contained in this query, if known up-front.
TermsEnum	getTermsEnum(Terms terms)	Constructs an enumeration that expands the pattern term.
protected abstract TermsEnum	getTermsEnum(Terms terms, AttributeSource atts)	Construct the enumeration to be used, expanding the pattern term.
int	hashCode()	Override and implement query hash code properly in a subclass.
Query	rewrite(IndexReader reader)	To rewrite to a simpler form, instead return a simpler enum from getTermsEnum(Terms, AttributeSource).
void	setRewriteMethod(MultiTermQuery.RewriteMethod method)	Deprecated. set this using a constructor instead

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

classHash, createWeight, sameClassAs, toString, toString, visit

Methods inherited from class java.lang.Object

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

Field Detail

field

protected final String field

rewriteMethod

protected MultiTermQuery.RewriteMethod rewriteMethod

CONSTANT_SCORE_BLENDED_REWRITE

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_BLENDED_REWRITE

A rewrite method where documents are assigned a constant score equal to the query's boost. Maintains a boolean query-like implementation over the most costly terms while pre-processing the less costly terms into a filter bitset. Enforces an upper-limit on the number of terms allowed in the boolean query-like implementation.

This method aims to balance the benefits of both CONSTANT_SCORE_BOOLEAN_REWRITE and CONSTANT_SCORE_REWRITE by enabling skipping and early termination over costly terms while limiting the overhead of a BooleanQuery with many terms. It also ensures you cannot hit IndexSearcher.TooManyClauses. For some use-cases with all low cost terms, CONSTANT_SCORE_REWRITE may be more performant. While for some use-cases with all high cost terms, CONSTANT_SCORE_BOOLEAN_REWRITE may be better.

CONSTANT_SCORE_REWRITE

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_REWRITE

A rewrite method that first creates a private Filter, by visiting each term in sequence and marking all docs for that term. Matching documents are assigned a constant score equal to the query's boost.

This method is faster than the BooleanQuery rewrite methods when the number of matched terms or matched documents is non-trivial. Also, it will never hit an errant IndexSearcher.TooManyClauses exception.

DOC_VALUES_REWRITE

public static final MultiTermQuery.RewriteMethod DOC_VALUES_REWRITE

A rewrite method that uses DocValuesType.SORTED / DocValuesType.SORTED_SET doc values to find matching docs through a post-filtering type approach. This will be very slow if used in isolation, but will likely be the most performant option when combined with a sparse query clause. All matching docs are assigned a constant score equal to the query's boost.

If you don't have doc values indexed, see the other rewrite methods that rely on postings alone (e.g., CONSTANT_SCORE_BLENDED_REWRITE, SCORING_BOOLEAN_REWRITE, etc. depending on scoring needs).

SCORING_BOOLEAN_REWRITE

public static final MultiTermQuery.RewriteMethod SCORING_BOOLEAN_REWRITE

A rewrite method that first translates each term into BooleanClause.Occur.SHOULD clause in a BooleanQuery, and keeps the scores as computed by the query. Note that typically such scores are meaningless to the user, and require non-trivial CPU to compute, so it's almost always better to use CONSTANT_SCORE_REWRITE instead.

NOTE: This rewrite method will hit IndexSearcher.TooManyClauses if the number of terms exceeds IndexSearcher.getMaxClauseCount().

CONSTANT_SCORE_BOOLEAN_REWRITE

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_BOOLEAN_REWRITE

Like SCORING_BOOLEAN_REWRITE except scores are not computed. Instead, each matching document receives a constant score equal to the query's boost.

NOTE: This rewrite method will hit IndexSearcher.TooManyClauses if the number of terms exceeds IndexSearcher.getMaxClauseCount().

Constructor Detail

MultiTermQuery

public MultiTermQuery(String field,
                      MultiTermQuery.RewriteMethod rewriteMethod)

Constructs a query matching terms that cannot be represented with a single Term.

Method Detail

getField

public final String getField()

Returns the field name for this query

getTermsEnum

protected abstract TermsEnum getTermsEnum(Terms terms,
                                          AttributeSource atts)
                                   throws IOException

Construct the enumeration to be used, expanding the pattern term. This method should only be called if the field exists (ie, implementations can assume the field does exist). This method should not return null (should instead return TermsEnum.EMPTY if no terms match). The TermsEnum must already be positioned to the first matching term. The given AttributeSource is passed by the MultiTermQuery.RewriteMethod to share information between segments, for example TopTermsRewrite uses it to share maximum competitive boosts

Throws:

IOException

getTermsEnum

public final TermsEnum getTermsEnum(Terms terms)
                             throws IOException

Constructs an enumeration that expands the pattern term. This method should only be called if the field exists (ie, implementations can assume the field does exist). This method never returns null. The returned TermsEnum is positioned to the first matching term.

Throws:

IOException

getTermsCount

public long getTermsCount()
                   throws IOException

Return the number of unique terms contained in this query, if known up-front. If not known, -1 will be returned.

Throws:

IOException

rewrite

public final Query rewrite(IndexReader reader)
                    throws IOException

To rewrite to a simpler form, instead return a simpler enum from getTermsEnum(Terms, AttributeSource). For example, to rewrite to a single term, return a SingleTermsEnum

Overrides:

rewrite in class Query

Throws:

IOException

See Also:

IndexSearcher.rewrite(Query)

getRewriteMethod

public MultiTermQuery.RewriteMethod getRewriteMethod()

setRewriteMethod

@Deprecated
public void setRewriteMethod(MultiTermQuery.RewriteMethod method)

Deprecated.

set this using a constructor instead

Sets the rewrite method to be used when executing the query. You can use one of the four core methods, or implement your own subclass of MultiTermQuery.RewriteMethod.

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()