org.apache.lucene.search

## Class CombinedFieldQuery

- java.lang.Object
- - org.apache.lucene.search.Query
  - - org.apache.lucene.search.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.

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `CombinedFieldQuery.Builder` A builder for `CombinedFieldQuery`.

  - ### Field Summary

    - ### Fields inherited from interface org.apache.lucene.util.Accountable

      `NULL_ACCOUNTABLE`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `Weight` | `createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)`
    `boolean` | `equals(Object o)`
    `List<Term>` | `getTerms()`
    `int` | `hashCode()`
    `long` | `ramBytesUsed()`
    `Query` | `rewrite(IndexReader reader)`
    `String` | `toString(String field)`
    `void` | `visit(QueryVisitor visitor)`

    - ### Methods inherited from class org.apache.lucene.search.Query

      `classHash, sameClassAs, toString`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface org.apache.lucene.util.Accountable

      `getChildResources`

- - ### Method Detail

    - #### getTerms

          public List<Term> getTerms()

    - #### toString

          public String toString(String field)

      Specified by:
        `toString` in class `Query`

    - #### equals

          public boolean equals(Object o)

      Specified by:
        `equals` in class `Query`

    - #### hashCode

          public int hashCode()

      Specified by:
        `hashCode` in class `Query`

    - #### ramBytesUsed

          public long ramBytesUsed()

      Specified by:
        `ramBytesUsed` in interface `Accountable`

    - #### rewrite

          public Query rewrite(IndexReader reader)
                        throws IOException

      Overrides:
        `rewrite` in class `Query`
      Throws:
        `IOException`

    - #### visit

          public void visit(QueryVisitor visitor)

      Overrides:
        `visit` in class `Query`

    - #### createWeight

          public Weight createWeight(IndexSearcher searcher,
                                     ScoreMode scoreMode,
                                     float boost)
                              throws IOException

      Overrides:
        `createWeight` in class `Query`
      Throws:
        `IOException`

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