Package org.apache.lucene.search

Class BlendedTermQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.BlendedTermQuery

public final class BlendedTermQuery
extends Query

A Query that blends index statistics across multiple terms. This is particularly useful when several terms should produce identical scores, regardless of their index statistics.

For instance imagine that you are resolving synonyms at search time, all terms should produce identical scores instead of the default behavior, which tends to give higher scores to rare terms.

An other useful use-case is cross-field search: imagine that you would like to search for john on two fields: first_name and last_name. You might not want to give a higher weight to matches on the field where john is rarer, in which case BlendedTermQuery would help as well.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	BlendedTermQuery.Builder	A Builder for BlendedTermQuery.
static class	BlendedTermQuery.DisjunctionMaxRewrite	A BlendedTermQuery.RewriteMethod that creates a DisjunctionMaxQuery out of the sub queries.
static class	BlendedTermQuery.RewriteMethod	A BlendedTermQuery.RewriteMethod defines how queries for individual terms should be merged.

Field Summary

Fields

Modifier and Type	Field	Description
static final BlendedTermQuery.RewriteMethod	BOOLEAN_REWRITE	A BlendedTermQuery.RewriteMethod that adds all sub queries to a BooleanQuery.
static final BlendedTermQuery.RewriteMethod	DISJUNCTION_MAX_REWRITE	BlendedTermQuery.DisjunctionMaxRewrite instance with a tie-breaker of 0.01.

Method Summary

Modifier and Type	Method	Description
boolean	equals(Object other)	Override and implement query instance equivalence properly in a subclass.
int	hashCode()	Override and implement query hash code properly in a subclass.
final 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

Field Details

BOOLEAN_REWRITE

public static final BlendedTermQuery.RewriteMethod BOOLEAN_REWRITE

A BlendedTermQuery.RewriteMethod that adds all sub queries to a BooleanQuery. This BlendedTermQuery.RewriteMethod is useful when matching on several fields is considered better than having a good match on a single field.

DISJUNCTION_MAX_REWRITE

public static final BlendedTermQuery.RewriteMethod DISJUNCTION_MAX_REWRITE

BlendedTermQuery.DisjunctionMaxRewrite instance with a tie-breaker of 0.01.

Method Details

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)

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

rewrite

public final 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