public class

DisjunctionMaxQuery

extends Query
implements Iterable<T>
java.lang.Object
   ↳ org.apache.lucene.search.Query
     ↳ org.apache.lucene.search.DisjunctionMaxQuery

Class Overview

A query that generates the union of documents produced by its subqueries, and that scores each document with the maximum score for that document as produced by any subquery, plus a tie breaking increment for any additional matching subqueries. This is useful when searching for a word in multiple fields with different boost factors (so that the fields cannot be combined equivalently into a single search field). We want the primary score to be the one associated with the highest boost, not the sum of the field scores (as BooleanQuery would give). If the query is "albino elephant" this ensures that "albino" matching one field and "elephant" matching another gets a higher score than "albino" matching both fields. To get this result, use both BooleanQuery and DisjunctionMaxQuery: for each term a DisjunctionMaxQuery searches for it in each field, while the set of these DisjunctionMaxQuery's is combined into a BooleanQuery. The tie breaker capability allows results that include the same term in multiple fields to be judged better than results that include this term in only the best of those multiple fields, without confusing this with the better case of two different terms in the multiple fields.

Summary

Nested Classes
class DisjunctionMaxQuery.DisjunctionMaxWeight Expert: the Weight for DisjunctionMaxQuery, used to normalize, score and explain these queries. 
Public Constructors
DisjunctionMaxQuery(float tieBreakerMultiplier)
Creates a new empty DisjunctionMaxQuery.
DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier)
Creates a new DisjunctionMaxQuery
Public Methods
void add(Query query)
Add a subquery to this disjunction
void add(Collection<Query> disjuncts)
Add a collection of disjuncts to this disjunction via Iterable
Object clone()
Create a shallow copy of us -- used in rewriting if necessary
Weight createWeight(Searcher searcher)
Create the Weight used to score us
boolean equals(Object o)
Return true iff we represent the same query as o
void extractTerms(Set<Term> terms)
Expert: adds all terms occurring in this query to the terms set.
int hashCode()
Compute a hash code for hashing us
Iterator<Query> iterator()
An Iterator over the disjuncts
Query rewrite(IndexReader reader)
Optimize our representation and our subqueries representations
String toString(String field)
Prettyprint us.
[Expand]
Inherited Methods
From class org.apache.lucene.search.Query
From class java.lang.Object
From interface java.lang.Iterable

Public Constructors

public DisjunctionMaxQuery (float tieBreakerMultiplier)

Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.

Parameters
tieBreakerMultiplier the score of each non-maximum disjunct for a document is multiplied by this weight and added into the final score. If non-zero, the value should be small, on the order of 0.1, which says that 10 occurrences of word in a lower-scored field that is also in a higher scored field is just as good as a unique word in the lower scored field (i.e., one that is not in any higher scored field.

public DisjunctionMaxQuery (Collection<Query> disjuncts, float tieBreakerMultiplier)

Creates a new DisjunctionMaxQuery

Parameters
disjuncts a Collection of all the disjuncts to add
tieBreakerMultiplier the weight to give to each matching non-maximum disjunct

Public Methods

public void add (Query query)

Add a subquery to this disjunction

Parameters
query the disjunct added

public void add (Collection<Query> disjuncts)

Add a collection of disjuncts to this disjunction via Iterable

public Object clone ()

Create a shallow copy of us -- used in rewriting if necessary

Returns
  • a copy of us (but reuse, don't copy, our subqueries)

public Weight createWeight (Searcher searcher)

Create the Weight used to score us

Throws
IOException

public boolean equals (Object o)

Return true iff we represent the same query as o

Parameters
o another object
Returns
  • true iff o is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us

public void extractTerms (Set<Term> terms)

Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.

public int hashCode ()

Compute a hash code for hashing us

Returns
  • the hash code

public Iterator<Query> iterator ()

An Iterator over the disjuncts

public Query rewrite (IndexReader reader)

Optimize our representation and our subqueries representations

Parameters
reader the IndexReader we query
Returns
  • an optimized copy of us (which may not be a copy if there is nothing to optimize)
Throws
IOException

public String toString (String field)

Prettyprint us.

Parameters
field the field to which we are applied
Returns
  • a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"