Package org.apache.lucene.search

# Class FuzzyQuery

java.lang.Object
org.apache.lucene.search.Query
org.apache.lucene.search.MultiTermQuery
org.apache.lucene.search.FuzzyQuery

public class FuzzyQuery extends MultiTermQuery
Implements the fuzzy search query. The similarity measurement is based on the Damerau-Levenshtein (optimal string alignment) algorithm, though you can explicitly choose classic Levenshtein by passing `false` to the `transpositions` parameter.

This query uses `MultiTermQuery.TopTermsBlendedFreqScoringRewrite` as default. So terms will be collected and scored according to their edit distance. Only the top terms are used for building the `BooleanQuery`. It is not recommended to change the rewrite mode for fuzzy queries.

At most, this query will match terms up to 2 edits. Higher distances (especially with transpositions enabled), are generally not useful and will match a significant amount of the term dictionary. If you really want this, consider using an n-gram indexing technique (such as the SpellChecker in the suggest module) instead.

NOTE: terms of length 1 or 2 will sometimes not match because of how the scaled distance between two terms is computed. For a term to match, the edit distance between the terms must be less than the minimum length term (either the input term, or the candidate term). For example, FuzzyQuery on term "abcd" with maxEdits=2 will not match an indexed term "ab", and FuzzyQuery on term "a" with maxEdits=2 will not match an indexed term "abc".

## Nested Class Summary

## Nested classes/interfaces inherited from class org.apache.lucene.search.MultiTermQuery

`MultiTermQuery.RewriteMethod, MultiTermQuery.TopTermsBlendedFreqScoringRewrite, MultiTermQuery.TopTermsBoostOnlyBooleanQueryRewrite, MultiTermQuery.TopTermsScoringBooleanQueryRewrite`

## Field Summary

Fields
Modifier and Type
Field
Description
`static final int`
`defaultMaxEdits`
`static final int`
`defaultMaxExpansions`
`static final int`
`defaultPrefixLength`
`static final boolean`
`defaultTranspositions`

### Fields inherited from class org.apache.lucene.search.MultiTermQuery

`CONSTANT_SCORE_BLENDED_REWRITE, CONSTANT_SCORE_BOOLEAN_REWRITE, CONSTANT_SCORE_REWRITE, DOC_VALUES_REWRITE, field, rewriteMethod, SCORING_BOOLEAN_REWRITE`

## Constructor Summary

Constructors
Constructor
Description
`FuzzyQuery(Term term)`
Calls `FuzzyQuery(term, defaultMaxEdits)`.
`FuzzyQuery(Term term, int maxEdits)`
Calls `FuzzyQuery(term, maxEdits, defaultPrefixLength)`.
`FuzzyQuery(Term term, int maxEdits, int prefixLength)`
Calls `FuzzyQuery(term, maxEdits, prefixLength, defaultMaxExpansions, defaultTranspositions)`.
`FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions)`
Calls `FuzzyQuery(Term, int, int, int, boolean, org.apache.lucene.search.MultiTermQuery.RewriteMethod)` FuzzyQuery(term, maxEdits, prefixLength, maxExpansions, defaultRewriteMethod(maxExpansions))
`FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions, MultiTermQuery.RewriteMethod rewriteMethod)`
Create a new FuzzyQuery that will match terms with an edit distance of at most `maxEdits` to `term`.

## Method Summary

Modifier and Type
Method
Description
`static MultiTermQuery.RewriteMethod`
`defaultRewriteMethod(int maxExpansions)`
Creates a default top-terms blended frequency scoring rewrite with the given max expansions
`boolean`
`equals(Object obj)`
Override and implement query instance equivalence properly in a subclass.
`static int`
`floatToEdits(float minimumSimilarity, int termLen)`
Helper function to convert from "minimumSimilarity" fractions to raw edit distances.
`CompiledAutomaton`
`getAutomata()`
Returns the compiled automata used to match terms
`static CompiledAutomaton`
`getFuzzyAutomaton(String term, int maxEdits, int prefixLength, boolean transpositions)`
Returns the `CompiledAutomaton` internally used by `FuzzyQuery` to match terms.
`int`
`getMaxEdits()`
`int`
`getPrefixLength()`
Returns the non-fuzzy prefix length.
`Term`
`getTerm()`
Returns the pattern term.
`protected TermsEnum`
`getTermsEnum(Terms terms, AttributeSource atts)`
Construct the enumeration to be used, expanding the pattern term.
`boolean`
`getTranspositions()`
Returns true if transpositions should be treated as a primitive edit operation.
`int`
`hashCode()`
Override and implement query hash code properly in a subclass.
`String`
`toString(String field)`
Prints a query to a string, with `field` assumed to be the default field and omitted.
`void`
`visit(QueryVisitor visitor)`
Recurse through the query tree, visiting any child queries.

### Methods inherited from class org.apache.lucene.search.MultiTermQuery

`getField, getRewriteMethod, getTermsCount, getTermsEnum, rewrite`

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

`classHash, createWeight, sameClassAs, toString`

### Methods inherited from class java.lang.Object

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

## Field Details

### defaultMaxEdits

public static final int defaultMaxEdits

See Also:
  - Constant Field Values

### defaultPrefixLength

public static final int defaultPrefixLength

See Also:
  - Constant Field Values

### defaultMaxExpansions

public static final int defaultMaxExpansions

See Also:
  - Constant Field Values

### defaultTranspositions

public static final boolean defaultTranspositions

See Also:
  - Constant Field Values

## Constructor Details

### FuzzyQuery

public FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions, MultiTermQuery.RewriteMethod rewriteMethod)
Create a new FuzzyQuery that will match terms with an edit distance of at most `maxEdits` to `term`. If a `prefixLength` > 0 is specified, a common prefix of that length is also required.

Parameters:
  `term` - the term to search for
  `maxEdits` - must be `>= 0` and `<=` `LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE`.
  `prefixLength` - length of common (non-fuzzy) prefix
  `maxExpansions` - the maximum number of terms to match. If this number is greater than `IndexSearcher.getMaxClauseCount()` when the query is rewritten, then the maxClauseCount will be used instead.
  `transpositions` - true if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.
  `rewriteMethod` - the rewrite method to use to build the final query

### FuzzyQuery

public FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions)
Calls `FuzzyQuery(Term, int, int, int, boolean, org.apache.lucene.search.MultiTermQuery.RewriteMethod)` FuzzyQuery(term, maxEdits, prefixLength, maxExpansions, defaultRewriteMethod(maxExpansions))

### FuzzyQuery

public FuzzyQuery(Term term, int maxEdits, int prefixLength)
Calls `FuzzyQuery(term, maxEdits, prefixLength, defaultMaxExpansions, defaultTranspositions)`.

### FuzzyQuery

public FuzzyQuery(Term term, int maxEdits)
Calls `FuzzyQuery(term, maxEdits, defaultPrefixLength)`.

### FuzzyQuery

public FuzzyQuery(Term term)
Calls `FuzzyQuery(term, defaultMaxEdits)`.

## Method Details

### defaultRewriteMethod

public static MultiTermQuery.RewriteMethod defaultRewriteMethod(int maxExpansions)
Creates a default top-terms blended frequency scoring rewrite with the given max expansions

### getMaxEdits

public int getMaxEdits()

Returns:
  the maximum number of edit distances allowed for this query to match.

### getPrefixLength

public int getPrefixLength()
Returns the non-fuzzy prefix length. This is the number of characters at the start of a term that must be identical (not fuzzy) to the query term if the query is to match that term.

### getTranspositions

public boolean getTranspositions()
Returns true if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.

### getAutomata

public CompiledAutomaton getAutomata()
Returns the compiled automata used to match terms

### getFuzzyAutomaton

public static CompiledAutomaton getFuzzyAutomaton(String term, int maxEdits, int prefixLength, boolean transpositions)
Returns the `CompiledAutomaton` internally used by `FuzzyQuery` to match terms. This is a very low-level method and may no longer exist in case the implementation of fuzzy-matching changes in the future.

Parameters:
  `term` - the term to search for
  `maxEdits` - must be `>= 0` and `<=` `LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE`.
  `prefixLength` - length of common (non-fuzzy) prefix
  `transpositions` - true if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.
Returns:
  A `CompiledAutomaton` that matches terms that satisfy input parameters.
NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

### visit

public void visit(QueryVisitor visitor)
Description copied from class: `Query`
Recurse through the query tree, visiting any child queries.

Specified by:
  `visit` in class `Query`
Parameters:
  `visitor` - a QueryVisitor to be called by each query in the tree

### getTermsEnum

protected TermsEnum getTermsEnum(Terms terms, AttributeSource atts) throws IOException
Description copied from class: `MultiTermQuery`
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

Specified by:
  `getTermsEnum` in class `MultiTermQuery`
Throws:
  `IOException`

### getTerm

public Term getTerm()
Returns the pattern term.

### toString

public String toString(String field)
Description copied from class: `Query`
Prints a query to a string, with `field` assumed to be the default field and omitted.

Specified by:
  `toString` in class `Query`

### 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.

Overrides:
  `hashCode` in class `MultiTermQuery`
See Also:
  - `Query.equals(Object)`

### equals

public boolean equals(Object obj)
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 to those of the other instance. Utility methods are provided for certain repetitive code.

Overrides:
  `equals` in class `MultiTermQuery`
See Also:
  - `Query.sameClassAs(Object)`
  - `Query.classHash()`

### floatToEdits

public static int floatToEdits(float minimumSimilarity, int termLen)
Helper function to convert from "minimumSimilarity" fractions to raw edit distances.

Parameters:
  `minimumSimilarity` - scaled similarity
  `termLen` - length (in unicode codepoints) of the term.
Returns:
  equivalent number of maxEdits