Package org.apache.lucene.search

Class NGramPhraseQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.NGramPhraseQuery

public class NGramPhraseQuery
extends Query

This is a PhraseQuery which is optimized for n-gram phrase query. For example, when you query "ABCD" on a 2-gram field, you may want to use NGramPhraseQuery rather than PhraseQuery, because NGramPhraseQuery will Query.rewrite(IndexSearcher) the query to "AB/0 CD/2", while PhraseQuery will query "AB/0 BC/1 CD/2" (where term/position).

Constructor Summary

Constructors

Constructor	Description
NGramPhraseQuery(int n, PhraseQuery query)	Constructor that takes gram size.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object other)	Override and implement query instance equivalence properly in a subclass.
int	getN()	Return the n in n-gram
int[]	getPositions()	Return the list of relative positions that each term should appear at.
Term[]	getTerms()	Return the list of terms.
int	hashCode()	Override and implement query hash code properly in a subclass.
Query	rewrite(IndexSearcher indexSearcher)	Expert: called to re-write queries into primitive queries.
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.Query

classHash, createWeight, rewrite, sameClassAs, toString

Methods inherited from class java.lang.Object

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

Constructor Details

NGramPhraseQuery

public NGramPhraseQuery(int n,
 PhraseQuery query)

Constructor that takes gram size.

Parameters:

n - n-gram size

Method Details

rewrite

public Query rewrite(IndexSearcher indexSearcher)
              throws IOException

Description copied from class: Query

Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

Callers are expected to call rewrite multiple times if necessary, until the rewritten query is the same as the original query.

The rewrite process may be able to make use of IndexSearcher's executor and be executed in parallel if the executor is provided.

However, if any of the intermediary queries do not satisfy the new API, parallel rewrite is not possible for any subsequent sub-queries. To take advantage of this API, the entire query tree must override this method.

Overrides:

rewrite in class Query

Throws:

IOException

See Also:

• IndexSearcher.rewrite(Query)

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

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 to those of the other instance. Utility methods are provided for certain repetitive code.

Specified by:

equals in class Query

See Also:

• Query.sameClassAs(Object)
• Query.classHash()

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)

getN

public int getN()

Return the n in n-gram

getTerms

public Term[] getTerms()

Return the list of terms.

getPositions

public int[] getPositions()

Return the list of relative positions that each term should appear at.

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