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java.lang.Object org.apache.lucene.search.Query org.apache.lucene.search.DisjunctionMaxQuery
public class DisjunctionMaxQuery
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.
Nested Class Summary | |
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protected class |
DisjunctionMaxQuery.DisjunctionMaxWeight
Expert: the Weight for DisjunctionMaxQuery, used to normalize, score and explain these queries. |
Constructor Summary | |
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DisjunctionMaxQuery(Collection<Query> disjuncts,
float tieBreakerMultiplier)
Creates a new DisjunctionMaxQuery |
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DisjunctionMaxQuery(float tieBreakerMultiplier)
Creates a new empty DisjunctionMaxQuery. |
Method Summary | |
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void |
add(Collection<Query> disjuncts)
Add a collection of disjuncts to this disjunction via Iterable |
void |
add(Query query)
Add a subquery to this disjunction |
Object |
clone()
Create a shallow copy of us -- used in rewriting if necessary |
Weight |
createWeight(Searcher searcher)
Expert: Constructs an appropriate Weight implementation for this query. |
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 |
Query |
rewrite(IndexReader reader)
Optimize our representation and our subqueries representations |
String |
toString(String field)
Prettyprint us. |
Methods inherited from class org.apache.lucene.search.Query |
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combine, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, weight |
Methods inherited from class java.lang.Object |
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finalize, getClass, notify, notifyAll, wait, wait, wait |
Constructor Detail |
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public DisjunctionMaxQuery(float tieBreakerMultiplier)
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)
disjuncts
- a CollectiontieBreakerMultiplier
- the weight to give to each matching non-maximum disjunctMethod Detail |
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public void add(Query query)
query
- the disjunct addedpublic void add(Collection<Query> disjuncts)
public Iterator<Query> iterator()
iterator
in interface Iterable<Query>
public Weight createWeight(Searcher searcher) throws IOException
Query
Only implemented by primitive queries, which re-write to themselves.
createWeight
in class Query
IOException
public Query rewrite(IndexReader reader) throws IOException
rewrite
in class Query
reader
- the IndexReader we query
IOException
public Object clone()
clone
in class Query
public void extractTerms(Set<Term> terms)
Query
rewritten
form.
extractTerms
in class Query
public String toString(String field)
toString
in class Query
field
- the field to which we are applied
public boolean equals(Object o)
equals
in class Query
o
- another object
public int hashCode()
hashCode
in class Query
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