Package org.apache.lucene.search

Class DisjunctionMaxQuery

java.lang.Object
org.apache.lucene.search.Query
org.apache.lucene.search.DisjunctionMaxQuery
All Implemented Interfaces:
Cloneable, Iterable<Query>
public class DisjunctionMaxQuery extends Query implements Iterable<Query>
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.

  • Constructor Details

    • DisjunctionMaxQuery

      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.

    • DisjunctionMaxQuery

      public DisjunctionMaxQuery(Collection<Query> disjuncts, float tieBreakerMultiplier)
      Creates a new DisjunctionMaxQuery
      Parameters:
      disjuncts - a Collection<Query> of all the disjuncts to add
      tieBreakerMultiplier - the weight to give to each matching non-maximum disjunct

  • Method Details

    • add

      public void add(Query query)
      Add a subquery to this disjunction
      Parameters:
      query - the disjunct added

    • add

      public void add(Collection<Query> disjuncts)
      Add a collection of disjuncts to this disjunction via Iterable<Query>
      Parameters:
      disjuncts - a collection of queries to add as disjuncts.

    • iterator

      public Iterator<Query> iterator()
      Specified by:
      iterator in interface Iterable<Query>
      Returns:
      An Iterator<Query> over the disjuncts

    • getDisjuncts

      public ArrayList<Query> getDisjuncts()
      Returns:
      the disjuncts.

    • getTieBreakerMultiplier

      public float getTieBreakerMultiplier()
      Returns:
      tie breaker value for multiple matches.

    • createWeight

      public Weight createWeight(IndexSearcher searcher) throws IOException
      Create the Weight used to score us
      Overrides:
      createWeight in class Query
      Throws:
      IOException

    • rewrite

      public Query rewrite(IndexReader reader) throws IOException
      Optimize our representation and our subqueries representations
      Overrides:
      rewrite in class Query
      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

    • clone

      public DisjunctionMaxQuery clone()
      Create a shallow copy of us -- used in rewriting if necessary
      Overrides:
      clone in class Query
      Returns:
      a copy of us (but reuse, don't copy, our subqueries)

    • extractTerms

      public void extractTerms(Set<Term> terms)
      Description copied from class: Query
      Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.
      Overrides:
      extractTerms in class Query

    • toString

      public String toString(String field)
      Prettyprint us.
      Specified by:
      toString in class Query
      Parameters:
      field - the field to which we are applied
      Returns:
      a string that shows what we do, of the form "(disjunct1 | disjunct2 | ... | disjunctn)^boost"

    • equals

      public boolean equals(Object o)
      Return true iff we represent the same query as o
      Overrides:
      equals in class Query
      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

    • hashCode

      public int hashCode()
      Compute a hash code for hashing us
      Overrides:
      hashCode in class Query
      Returns:
      the hash code