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, 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.

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