Package 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
All Implemented Interfaces:
Cloneable
public 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 Details

    • FieldMaskingSpanQuery

      public FieldMaskingSpanQuery(SpanQuery maskedQuery, String maskedField)

  • Method Details

    • getField

      public String getField()
      Description copied from class: SpanQuery
      Returns the name of the field matched by this query.

      Note that this may return null if the query matches no terms.

      Specified by:
      getField in class SpanQuery

    • getMaskedQuery

      public SpanQuery getMaskedQuery()

    • getSpans

      public Spans getSpans(AtomicReaderContext context, Bits acceptDocs, Map<Term,TermContext> termContexts) throws IOException
      Description copied from class: SpanQuery
      Expert: Returns the matches for this query in an index. Used internally to search for spans.
      Specified by:
      getSpans in class SpanQuery
      Throws:
      IOException

    • extractTerms

      public void extractTerms(Set<Term> terms)
      Description copied from class: Query
      Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.
      Overrides:
      extractTerms in class Query

    • createWeight

      public Weight createWeight(IndexSearcher searcher) 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 SpanQuery
      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 o)
      Overrides:
      equals in class Query

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Query