Class 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 Detail

      • DisjunctionMaxQuery

        public DisjunctionMaxQuery​(float tieBreakerMultiplier)
        Creates a new empty DisjunctionMaxQuery. Use add() to add the subqueries.
        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
        disjuncts - a Collection<Query> of all the disjuncts to add
        tieBreakerMultiplier - the weight to give to each matching non-maximum disjunct
    • Method Detail

      • add

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

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

        public ArrayList<Query> getDisjuncts()
        the disjuncts.
      • getTieBreakerMultiplier

        public float getTieBreakerMultiplier()
        tie breaker value for multiple matches.
      • rewrite

        public Query rewrite​(IndexReader reader)
                      throws IOException
        Optimize our representation and our subqueries representations
        rewrite in class Query
        reader - the IndexReader we query
        an optimized copy of us (which may not be a copy if there is nothing to optimize)
      • clone

        public DisjunctionMaxQuery clone()
        Create a shallow copy of us -- used in rewriting if necessary
        clone in class Query
        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.
        extractTerms in class Query
      • toString

        public String toString​(String field)
        Prettyprint us.
        Specified by:
        toString in class Query
        field - the field to which we are applied
        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
        equals in class Query
        o - another object
        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
        hashCode in class Query
        the hash code