Package org.apache.lucene.search

Class DisjunctionMaxQuery

java.lang.Object
org.apache.lucene.search.Query
org.apache.lucene.search.DisjunctionMaxQuery
All Implemented Interfaces:
Iterable<Query>
public final 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(Collection<Query> disjuncts, float tieBreakerMultiplier)
      Creates a new DisjunctionMaxQuery
      Parameters:
      disjuncts - a Collection<Query> of all the disjuncts to add
      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.

  • Method Details

    • iterator

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

    • getDisjuncts

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

    • getTieBreakerMultiplier

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

    • createWeight

      public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException
      Create the Weight used to score us
      Overrides:
      createWeight in class Query
      scoreMode - How the produced scorers will be consumed.
      boost - The boost that is propagated by the parent queries.
      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

    • 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

    • 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 other)
      Return true if we represent the same query as other
      Specified by:
      equals in class Query
      Parameters:
      other - another object
      Returns:
      true if other is a DisjunctionMaxQuery with the same boost and the same subqueries, in the same order, as us
      See Also:

    • hashCode

      public int hashCode()
      Compute a hash code for hashing us
      Specified by:
      hashCode in class Query
      Returns:
      the hash code
      See Also: