Package org.apache.lucene.search

Class 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 Detail

      • 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 Detail

      • 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

      • 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:
        Query.sameClassAs(Object), Query.classHash()