org.apache.lucene.search

Class MultiTermQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.MultiTermQuery

Direct Known Subclasses:

AutomatonQuery, FuzzyQuery

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 setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod) is either CONSTANT_SCORE_BOOLEAN_REWRITE or SCORING_BOOLEAN_REWRITE, you may encounter a BooleanQuery.TooManyClauses exception during searching, which happens when the number of terms to be searched exceeds BooleanQuery.getMaxClauseCount(). Setting setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod) to CONSTANT_SCORE_REWRITE prevents this.

The recommended rewrite method is CONSTANT_SCORE_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 and 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 and Description
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.
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 and Description
MultiTermQuery(String field) Constructs a query matching terms that cannot be represented with a single Term.

Method Summary

Modifier and Type	Method and 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()
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) Sets the rewrite method to be used when executing the query.

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_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 BooleanQuery.TooManyClauses exception.

See Also:

setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod)

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 BooleanQuery.TooManyClauses if the number of terms exceeds BooleanQuery.getMaxClauseCount().

See Also:

setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod)

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 BooleanQuery.TooManyClauses if the number of terms exceeds BooleanQuery.getMaxClauseCount().

See Also:

setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod)

Constructor Detail

MultiTermQuery

public MultiTermQuery(String field)

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

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

getRewriteMethod

public MultiTermQuery.RewriteMethod getRewriteMethod()

See Also:

setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod)

setRewriteMethod

public void setRewriteMethod(MultiTermQuery.RewriteMethod method)

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()