org.apache.lucene.search.spans

## Class FieldMaskingSpanQuery

- java.lang.Object
- - org.apache.lucene.search.Query
  - - org.apache.lucene.search.spans.SpanQuery
    - - org.apache.lucene.search.spans.FieldMaskingSpanQuery

-     public final class FieldMaskingSpanQuery
      extends SpanQuery

  Wrapper to allow `SpanQuery` objects participate in composite single-field SpanQueries by 'lying' about their search field. That is, the masked SpanQuery will function as normal, but `SpanQuery.getField()` simply hands back the value supplied in this class's constructor.

  This can be used to support Queries like `SpanNearQuery` or `SpanOrQuery` across different fields, which is not ordinarily permitted.

  This can be useful for denormalized relational data: for example, when indexing a document with conceptually many 'children':

        teacherid: 1
        studentfirstname: james
        studentsurname: jones

        teacherid: 2
        studenfirstname: james
        studentsurname: smith
        studentfirstname: sally
        studentsurname: jones

  a SpanNearQuery with a slop of 0 can be applied across two `SpanTermQuery` objects as follows:

          SpanQuery q1  = new SpanTermQuery(new Term("studentfirstname", "james"));
          SpanQuery q2  = new SpanTermQuery(new Term("studentsurname", "jones"));
          SpanQuery q2m = new FieldMaskingSpanQuery(q2, "studentfirstname");
          Query q = new SpanNearQuery(new SpanQuery[]{q1, q2m}, -1, false);

  to search for 'studentfirstname:james studentsurname:jones' and find teacherid 1 without matching teacherid 2 (which has a 'james' in position 0 and 'jones' in position 1).

  Note: as `getField()` returns the masked field, scoring will be done using the Similarity and collection statistics of the field name supplied, but with the term statistics of the real field. This may lead to exceptions, poor performance, and unexpected scoring behaviour.

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `FieldMaskingSpanQuery(SpanQuery maskedQuery, String maskedField)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `SpanWeight` | `createWeight(IndexSearcher searcher, boolean needsScores)` Expert: Constructs an appropriate Weight implementation for this query.
    `boolean` | `equals(Object other)` Override and implement query instance equivalence properly in a subclass.
    `String` | `getField()` Returns the name of the field matched by this query.
    `SpanQuery` | `getMaskedQuery()`
    `int` | `hashCode()` Override and implement query hash code properly in a subclass.
    `Query` | `rewrite(IndexReader reader)` 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.

    - ### Methods inherited from class org.apache.lucene.search.spans.SpanQuery

      `getTermContexts, getTermContexts`

    - ### 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

    - #### FieldMaskingSpanQuery

          public FieldMaskingSpanQuery(SpanQuery maskedQuery,
                                       String maskedField)

  - ### Method Detail

    - #### getField

          public String getField()

      Description copied from class: `SpanQuery`
      Returns the name of the field matched by this query.
      Specified by:
        `getField` in class `SpanQuery`

    - #### getMaskedQuery

          public SpanQuery getMaskedQuery()

    - #### createWeight

          public SpanWeight createWeight(IndexSearcher searcher,
                                         boolean needsScores)
                                  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.

      Specified by:
        `createWeight` in class `SpanQuery`
        `needsScores` - True if document scores (`Scorer.score()`) or match frequencies (`Scorer.freq()`) are needed.
      Throws:
        `IOException`

    - #### rewrite

          public Query rewrite(IndexReader reader)
                        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.
      Overrides:
        `rewrite` in class `Query`
      Throws:
        `IOException`

    - #### 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 other)

      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 that 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)`

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