org.apache.lucene.search.join

## Class ToParentBlockJoinQuery

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

-     public class ToParentBlockJoinQuery
      extends Query

  This query requires that you index children and parent docs as a single block, using the `IndexWriter.addDocuments()` or `IndexWriter.updateDocuments()` API. In each block, the child documents must appear first, ending with the parent document. At search time you provide a Filter identifying the parents, however this Filter must provide an `BitSet` per sub-reader.

  Once the block index is built, use this query to wrap any sub-query matching only child docs and join matches in that child document space up to the parent document space. You can then use this Query as a clause with other queries in the parent document space.

  See `ToChildBlockJoinQuery` if you need to join in the reverse order.

  The child documents must be orthogonal to the parent documents: the wrapped child query must never return a parent document.

  See `org.apache.lucene.search.join` for an overview.

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

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ToParentBlockJoinQuery(Query childQuery, BitSetProducer parentsFilter, ScoreMode scoreMode)` Create a ToParentBlockJoinQuery.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `Weight` | `createWeight(IndexSearcher searcher, boolean needsScores)`
    `boolean` | `equals(Object other)`
    `Query` | `getChildQuery()` Return our child query.
    `int` | `hashCode()`
    `Query` | `rewrite(IndexReader reader)`
    `String` | `toString(String field)`

    - ### 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`

- - ### Constructor Detail

    - #### ToParentBlockJoinQuery

          public ToParentBlockJoinQuery(Query childQuery,
                                        BitSetProducer parentsFilter,
                                        ScoreMode scoreMode)

      Create a ToParentBlockJoinQuery.
      Parameters:
        `childQuery` - Query matching child documents.
        `parentsFilter` - Filter identifying the parent documents.
        `scoreMode` - How to aggregate multiple child scores into a single parent score.

  - ### Method Detail

    - #### createWeight

          public Weight createWeight(IndexSearcher searcher,
                                     boolean needsScores)
                              throws IOException

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

    - #### getChildQuery

          public Query getChildQuery()

      Return our child query.

    - #### rewrite

          public Query rewrite(IndexReader reader)
                        throws IOException

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

    - #### toString

          public String toString(String field)

      Specified by:
        `toString` in class `Query`

    - #### equals

          public boolean equals(Object other)

      Specified by:
        `equals` in class `Query`

    - #### hashCode

          public int hashCode()

      Specified by:
        `hashCode` in class `Query`

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