org.apache.lucene.search
Class MultiTermQuery

java.lang.Object
  extended by org.apache.lucene.search.Query
      extended by org.apache.lucene.search.MultiTermQuery
All Implemented Interfaces:
Serializable, Cloneable
Direct Known Subclasses:
FuzzyQuery, NumericRangeQuery, PrefixQuery, RegexQuery, 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
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
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
MultiTermQuery()
          Constructs a query matching terms that cannot be represented with a single Term.
 
Method Summary
 void clearTotalNumberOfTerms()
          Expert: Resets the counting of unique terms.
 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()
          Expert: Return the number of unique terms visited during execution of the query.
 int hashCode()
           
protected  void incTotalNumberOfTerms(int inc)
           
 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

public int getTotalNumberOfTerms()
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 optimize 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 optimized indexes / no MultiReaders, you get the correct number of unique terms for the whole index. Use this number to compare different queries. For non-optimized 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

public void clearTotalNumberOfTerms()
Expert: Resets the counting of unique terms. Do this before executing the query/filter.

See Also:
getTotalNumberOfTerms()

incTotalNumberOfTerms

protected void incTotalNumberOfTerms(int inc)

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


Copyright © 2000-2011 Apache Software Foundation. All Rights Reserved.