Package org.apache.lucene.sandbox.search

Class CombinedFieldQuery

  • All Implemented Interfaces:
    Accountable
    public final class CombinedFieldQuery
extends Query
implements Accountable
    A Query that treats multiple fields as a single stream and scores terms as if you had indexed them as a single term in a single field.

    The query works as follows:

    1. Given a list of fields and weights, it pretends there is a synthetic combined field where all terms have been indexed. It computes new term and collection statistics for this combined field.
    2. It uses a disjunction iterator and IndexSearcher.getSimilarity() to score documents.

    In order for a similarity to be compatible, Similarity.computeNorm(org.apache.lucene.index.FieldInvertState) must be additive: the norm of the combined field is the sum of norms for each individual field. The norms must also be encoded using SmallFloat.intToByte4(int). These requirements hold for all similarities that compute norms the same way as SimilarityBase.computeNorm(org.apache.lucene.index.FieldInvertState), which includes BM25Similarity and DFRSimilarity. Per-field similarities are not supported.

    The query also requires that either all fields or no fields have norms enabled. Having only some fields with norms enabled can result in errors.

    The scoring is based on BM25F's simple formula described in: http://www.staff.city.ac.uk/~sb317/papers/foundations_bm25_review.pdf. This query implements the same approach but allows other similarities besides BM25Similarity.

    • Field Detail

      • BASE_RAM_BYTES

        private static final long BASE_RAM_BYTES

      • fieldTerms

        private final Term[] fieldTerms

      • ramBytesUsed

        private final long ramBytesUsed

    • Method Detail

      • getTerms

        public java.util.List<Term> getTerms()

      • toString

        public java.lang.String toString​(java.lang.String field)
        Description copied from class: Query
        Prints a query to a string, with field assumed to be the default field and omitted.
        Specified by:
        toString in class Query

      • equals

        public boolean equals​(java.lang.Object o)
        Description copied from class: Query
        Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly.

        Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.

        Specified by:
        equals in class Query
        See Also:
        Query.sameClassAs(Object), Query.classHash()

      • hashCode

        public int hashCode()
        Description copied from class: Query
        Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.
        Specified by:
        hashCode in class Query
        See Also:
        Query.equals(Object)

      • ramBytesUsed

        public long ramBytesUsed()
        Description copied from interface: Accountable
        Return the memory usage of this object in bytes. Negative values are illegal.
        Specified by:
        ramBytesUsed in interface Accountable

      • rewrite

        public Query rewrite​(IndexReader reader)
              throws java.io.IOException
        Description copied from class: Query
        Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

        Callers are expected to call rewrite multiple times if necessary, until the rewritten query is the same as the original query.

        Overrides:
        rewrite in class Query
        Throws:
        java.io.IOException
        See Also:
        IndexSearcher.rewrite(Query)

      • 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

      • rewriteToBoolean

        private BooleanQuery rewriteToBoolean()

      • createWeight

        public Weight createWeight​(IndexSearcher searcher,
                           ScoreMode scoreMode,
                           float boost)
                    throws java.io.IOException
        Description copied from class: Query
        Expert: Constructs an appropriate Weight implementation for this query.

        Only implemented by primitive queries, which re-write to themselves.

        Overrides:
        createWeight in class Query
        scoreMode - How the produced scorers will be consumed.
        boost - The boost that is propagated by the parent queries.
        Throws:
        java.io.IOException

      • validateConsistentNorms

        private void validateConsistentNorms​(IndexReader reader)