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.

    WARNING: This API is experimental and might change in incompatible ways in the next release.