org.apache.lucene.search

Class MultiTermQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.MultiTermQuery

All Implemented Interfaces:

Serializable, Cloneable

Direct Known Subclasses:

FuzzyQuery, NumericRangeQuery, PrefixQuery, TermRangeQuery, WildcardQuery

public abstract class MultiTermQuery
extends Query

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

This query cannot be used directly; you must subclass it and define getEnum(org.apache.lucene.index.IndexReader) to provide a FilteredTermEnum that iterates through the terms to be matched.

NOTE: if setRewriteMethod(org.apache.lucene.search.MultiTermQuery.RewriteMethod) is either CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE or SCORING_BOOLEAN_QUERY_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_FILTER_REWRITE prevents this.

The recommended rewrite method is CONSTANT_SCORE_AUTO_REWRITE_DEFAULT: it doesn't spend CPU computing unhelpful scores, and it tries to pick 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 QueryParser produces MultiTermQueries using CONSTANT_SCORE_AUTO_REWRITE_DEFAULT by default.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	MultiTermQuery.ConstantScoreAutoRewrite A rewrite method that tries to pick the best constant-score rewrite method based on term and document counts from the query.
static class	MultiTermQuery.RewriteMethod Abstract class that defines how the query is rewritten.
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_AUTO_REWRITE_DEFAULT Read-only default instance of MultiTermQuery.ConstantScoreAutoRewrite, with ConstantScoreAutoRewrite.setTermCountCutoff(int) set to ConstantScoreAutoRewrite.DEFAULT_TERM_COUNT_CUTOFF and ConstantScoreAutoRewrite.setDocCountPercent(double) set to ConstantScoreAutoRewrite.DEFAULT_DOC_COUNT_PERCENT.
static MultiTermQuery.RewriteMethod	CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE Like SCORING_BOOLEAN_QUERY_REWRITE except scores are not computed.
static MultiTermQuery.RewriteMethod	CONSTANT_SCORE_FILTER_REWRITE A rewrite method that first creates a private Filter, by visiting each term in sequence and marking all docs for that term.
protected MultiTermQuery.RewriteMethod	rewriteMethod
static MultiTermQuery.RewriteMethod	SCORING_BOOLEAN_QUERY_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() Constructs a query matching terms that cannot be represented with a single Term.

Method Summary

Methods

Modifier and Type	Method and Description
void	clearTotalNumberOfTerms() Deprecated. Don't use this method, as its not thread safe and useless.
boolean	equals(Object obj)
protected abstract FilteredTermEnum	getEnum(IndexReader reader) Construct the enumeration to be used, expanding the pattern term.
MultiTermQuery.RewriteMethod	getRewriteMethod()
int	getTotalNumberOfTerms() Deprecated. Don't use this method, as its not thread safe and useless.
int	hashCode()
protected void	incTotalNumberOfTerms(int inc) Deprecated. Don't use this method, as its not thread safe and useless.
Query	rewrite(IndexReader reader) To rewrite to a simpler form, instead return a simpler enum from getEnum(IndexReader).
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

clone, combine, createWeight, extractTerms, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, toString, weight

Methods inherited from class java.lang.Object

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

Field Detail

rewriteMethod

protected MultiTermQuery.RewriteMethod rewriteMethod

CONSTANT_SCORE_FILTER_REWRITE

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_FILTER_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_QUERY_REWRITE

public static final MultiTermQuery.RewriteMethod SCORING_BOOLEAN_QUERY_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_AUTO_REWRITE_DEFAULT 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_QUERY_REWRITE

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_BOOLEAN_QUERY_REWRITE

Like SCORING_BOOLEAN_QUERY_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)

CONSTANT_SCORE_AUTO_REWRITE_DEFAULT

public static final MultiTermQuery.RewriteMethod CONSTANT_SCORE_AUTO_REWRITE_DEFAULT

Read-only default instance of MultiTermQuery.ConstantScoreAutoRewrite, with ConstantScoreAutoRewrite.setTermCountCutoff(int) set to ConstantScoreAutoRewrite.DEFAULT_TERM_COUNT_CUTOFF and ConstantScoreAutoRewrite.setDocCountPercent(double) set to ConstantScoreAutoRewrite.DEFAULT_DOC_COUNT_PERCENT. Note that you cannot alter the configuration of this instance; you'll need to create a private instance instead.

Constructor Detail

MultiTermQuery

public MultiTermQuery()

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

Method Detail

getEnum

protected abstract FilteredTermEnum getEnum(IndexReader reader)
                                     throws IOException

Construct the enumeration to be used, expanding the pattern term.

Throws:

IOException

getTotalNumberOfTerms

@Deprecated
public int getTotalNumberOfTerms()

Deprecated. Don't use this method, as its not thread safe and useless.

Expert: Return the number of unique terms visited during execution of the query. If there are many of them, you may consider using another query type or reduce your total term count in index.

This method is not thread safe, be sure to only call it when no query is running! If you re-use the same query instance for another search, be sure to first reset the term counter with clearTotalNumberOfTerms().

On single-segment indexes / no MultiReaders, you get the correct number of unique terms for the whole index. Use this number to compare different queries. For multi-segment indexes this number can also be achieved in non-constant-score mode. In constant-score mode you get the total number of terms seeked for all segments / sub-readers.

See Also:

clearTotalNumberOfTerms()

clearTotalNumberOfTerms

@Deprecated
public void clearTotalNumberOfTerms()

Deprecated. Don't use this method, as its not thread safe and useless.

Expert: Resets the counting of unique terms. Do this before executing the query/filter.

See Also:

getTotalNumberOfTerms()

incTotalNumberOfTerms

@Deprecated
protected void incTotalNumberOfTerms(int inc)

Deprecated. Don't use this method, as its not thread safe and useless.

rewrite

public final Query rewrite(IndexReader reader)
                    throws IOException

To rewrite to a simpler form, instead return a simpler enum from getEnum(IndexReader). For example, to rewrite to a single term, return a SingleTermEnum

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()

Overrides:

hashCode in class Query

equals

public boolean equals(Object obj)

Overrides:

equals in class Query