Package 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 they had been indexed in a single field whose values would be the union of the values of the provided fields.

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 don't customize `Similarity.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.

This query assumes that all fields share the same analyzer. Scores may not make much sense if all fields don't have the same analyzer.

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
  Description
  `static class`
  `CombinedFieldQuery.Builder`
  A builder for `CombinedFieldQuery`.

- ## Field Summary

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

  `NULL_ACCOUNTABLE`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Weight`
  `createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)`
  Expert: Constructs an appropriate Weight implementation for this query.
  `boolean`
  `equals(Object o)`
  Override and implement query instance equivalence properly in a subclass.
  `int`
  `hashCode()`
  Override and implement query hash code properly in a subclass.
  `long`
  `ramBytesUsed()`
  Return the memory usage of this object in bytes.
  `Query`
  `rewrite(IndexSearcher indexSearcher)`
  Expert: called to re-write queries into primitive queries.
  `String`
  `toString(String field)`
  Prints a query to a string, with `field` assumed to be the default field and omitted.
  `void`
  `visit(QueryVisitor visitor)`
  Recurse through the query tree, visiting any child queries.

  ### 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 Details

  - ### toString

    public String toString(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(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 to those of the 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(IndexSearcher indexSearcher) throws 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.

    The rewrite process may be able to make use of IndexSearcher's executor and be executed in parallel if the executor is provided.

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

  - ### createWeight

    public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws 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`
    Parameters:
      `scoreMode` - How the produced scorers will be consumed.
      `boost` - The boost that is propagated by the parent queries.
    Throws:
      `IOException`