Class MultiTermQuery
- Direct Known Subclasses:
AutomatonQuery,FuzzyQuery,TermInSetQuery
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.
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic classAbstract class that defines how the query is rewritten.static final classA rewrite method that first translates each term intoBooleanClause.Occur.SHOULDclause 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 final classA rewrite method that first translates each term intoBooleanClause.Occur.SHOULDclause in a BooleanQuery, but the scores are only computed as the boost.static final classA rewrite method that first translates each term intoBooleanClause.Occur.SHOULDclause in a BooleanQuery, and keeps the scores as computed by the query. -
Field Summary
FieldsModifier and TypeFieldDescriptionstatic final MultiTermQuery.RewriteMethodA rewrite method where documents are assigned a constant score equal to the query's boost.static final MultiTermQuery.RewriteMethodLikeSCORING_BOOLEAN_REWRITEexcept scores are not computed.static final MultiTermQuery.RewriteMethodA rewrite method that first creates a private Filter, by visiting each term in sequence and marking all docs for that term.static final MultiTermQuery.RewriteMethodA rewrite method that usesDocValuesType.SORTED/DocValuesType.SORTED_SETdoc values to find matching docs through a post-filtering type approach.protected final Stringprotected final MultiTermQuery.RewriteMethodstatic final MultiTermQuery.RewriteMethodA rewrite method that first translates each term intoBooleanClause.Occur.SHOULDclause in a BooleanQuery, and keeps the scores as computed by the query. -
Constructor Summary
ConstructorsConstructorDescriptionMultiTermQuery(String field, MultiTermQuery.RewriteMethod rewriteMethod) Constructs a query matching terms that cannot be represented with a single Term. -
Method Summary
Modifier and TypeMethodDescriptionbooleanOverride and implement query instance equivalence properly in a subclass.final StringgetField()Returns the field name for this querylongReturn the number of unique terms contained in this query, if known up-front.final TermsEnumgetTermsEnum(Terms terms) Constructs an enumeration that expands the pattern term.protected abstract TermsEnumgetTermsEnum(Terms terms, AttributeSource atts) Construct the enumeration to be used, expanding the pattern term.inthashCode()Override and implement query hash code properly in a subclass.final Queryrewrite(IndexSearcher indexSearcher) To rewrite to a simpler form, instead return a simpler enum fromgetTermsEnum(Terms, AttributeSource).Methods inherited from class org.apache.lucene.search.Query
classHash, createWeight, sameClassAs, toString, toString, visit
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Field Details
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field
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rewriteMethod
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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_REWRITEandCONSTANT_SCORE_REWRITEby enabling skipping and early termination over costly terms while limiting the overhead of a BooleanQuery with many terms. It also ensures you cannot hitIndexSearcher.TooManyClauses. For some use-cases with all low cost terms,CONSTANT_SCORE_REWRITEmay be more performant. While for some use-cases with all high cost terms,CONSTANT_SCORE_BOOLEAN_REWRITEmay be better. -
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.TooManyClausesexception. -
DOC_VALUES_REWRITE
A rewrite method that usesDocValuesType.SORTED/DocValuesType.SORTED_SETdoc 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
A rewrite method that first translates each term intoBooleanClause.Occur.SHOULDclause 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 useCONSTANT_SCORE_REWRITEinstead.NOTE: This rewrite method will hit
IndexSearcher.TooManyClausesif the number of terms exceedsIndexSearcher.getMaxClauseCount(). -
CONSTANT_SCORE_BOOLEAN_REWRITE
LikeSCORING_BOOLEAN_REWRITEexcept 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.TooManyClausesif the number of terms exceedsIndexSearcher.getMaxClauseCount().
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Constructor Details
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MultiTermQuery
Constructs a query matching terms that cannot be represented with a single Term.
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Method Details
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getField
Returns the field name for this query -
getTermsEnum
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 returnTermsEnum.EMPTYif no terms match). The TermsEnum must already be positioned to the first matching term. The givenAttributeSourceis passed by theMultiTermQuery.RewriteMethodto share information between segments, for exampleTopTermsRewriteuses it to share maximum competitive boosts- Throws:
IOException
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getTermsEnum
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
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getTermsCount
public long getTermsCount()Return the number of unique terms contained in this query, if known up-front. If not known, -1 will be returned. -
rewrite
To rewrite to a simpler form, instead return a simpler enum fromgetTermsEnum(Terms, AttributeSource). For example, to rewrite to a single term, return aSingleTermsEnum- Overrides:
rewritein classQuery- Throws:
IOException- See Also:
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getRewriteMethod
- Returns:
- the rewrite method used to build the final query
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hashCode
public int hashCode()Description copied from class:QueryOverride and implement query hash code properly in a subclass. This is required so thatQueryCacheworks properly. -
equals
Description copied from class:QueryOverride and implement query instance equivalence properly in a subclass. This is required so thatQueryCacheworks 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.
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