org.apache.lucene.queries

## Class CustomScoreProvider

- java.lang.Object
- - org.apache.lucene.queries.CustomScoreProvider

-     public class CustomScoreProvider
      extends Object

  An instance of this subclass should be returned by `CustomScoreQuery.getCustomScoreProvider(org.apache.lucene.index.AtomicReaderContext)`, if you want to modify the custom score calculation of a `CustomScoreQuery`.

  Since Lucene 2.9, queries operate on each segment of an index separately, so the protected `context` field can be used to resolve doc IDs, as the supplied `doc` ID is per-segment and without knowledge of the IndexReader you cannot access the document or `FieldCache`.

  Since:
    2.9.2
  WARNING: This API is experimental and might change in incompatible ways in the next release.

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected AtomicReaderContext` | `context`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `CustomScoreProvider(AtomicReaderContext context)` Creates a new instance of the provider class for the given `IndexReader`.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `Explanation` | `customExplain(int doc, Explanation subQueryExpl, Explanation valSrcExpl)` Explain the custom score.
    `Explanation` | `customExplain(int doc, Explanation subQueryExpl, Explanation[] valSrcExpls)` Explain the custom score.
    `float` | `customScore(int doc, float subQueryScore, float valSrcScore)` Compute a custom score by the subQuery score and the `FunctionQuery` score.
    `float` | `customScore(int doc, float subQueryScore, float[] valSrcScores)` Compute a custom score by the subQuery score and a number of `FunctionQuery` scores.

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

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### context

          protected final AtomicReaderContext context

  - ### Constructor Detail

    - #### CustomScoreProvider

          public CustomScoreProvider(AtomicReaderContext context)

      Creates a new instance of the provider class for the given `IndexReader`.

  - ### Method Detail

    - #### customScore

          public float customScore(int doc,
                          float subQueryScore,
                          float[] valSrcScores)
                            throws IOException

      Compute a custom score by the subQuery score and a number of `FunctionQuery` scores.

      Subclasses can override this method to modify the custom score.

      If your custom scoring is different than the default herein you should override at least one of the two customScore() methods. If the number of `function queries` is always < 2 it is sufficient to override the other `customScore()` method, which is simpler.

      The default computation herein is a multiplication of given scores:

               ModifiedScore = valSrcScore * valSrcScores[0] * valSrcScores[1] * ...

      Parameters:
        `doc` - id of scored doc.
        `subQueryScore` - score of that doc by the subQuery.
        `valSrcScores` - scores of that doc by the `FunctionQuery`.
      Returns:
        custom score.
      Throws:
        `IOException`

    - #### customScore

          public float customScore(int doc,
                          float subQueryScore,
                          float valSrcScore)
                            throws IOException

      Compute a custom score by the subQuery score and the `FunctionQuery` score.

      Subclasses can override this method to modify the custom score.

      If your custom scoring is different than the default herein you should override at least one of the two customScore() methods. If the number of `function queries` is always < 2 it is sufficient to override this customScore() method, which is simpler.

      The default computation herein is a multiplication of the two scores:

               ModifiedScore = subQueryScore * valSrcScore

      Parameters:
        `doc` - id of scored doc.
        `subQueryScore` - score of that doc by the subQuery.
        `valSrcScore` - score of that doc by the `FunctionQuery`.
      Returns:
        custom score.
      Throws:
        `IOException`

    - #### customExplain

          public Explanation customExplain(int doc,
                                  Explanation subQueryExpl,
                                  Explanation[] valSrcExpls)
                                    throws IOException

      Explain the custom score. Whenever overriding `customScore(int, float, float[])`, this method should also be overridden to provide the correct explanation for the part of the custom scoring.
      Parameters:
        `doc` - doc being explained.
        `subQueryExpl` - explanation for the sub-query part.
        `valSrcExpls` - explanation for the value source part.
      Returns:
        an explanation for the custom score
      Throws:
        `IOException`

    - #### customExplain

          public Explanation customExplain(int doc,
                                  Explanation subQueryExpl,
                                  Explanation valSrcExpl)
                                    throws IOException

      Explain the custom score. Whenever overriding `customScore(int, float, float)`, this method should also be overridden to provide the correct explanation for the part of the custom scoring.
      Parameters:
        `doc` - doc being explained.
        `subQueryExpl` - explanation for the sub-query part.
        `valSrcExpl` - explanation for the value source part.
      Returns:
        an explanation for the custom score
      Throws:
        `IOException`

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