public class

FieldMaskingSpanQuery

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

Class Overview

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 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 norms of the field name supplied. This may lead to unexpected scoring behaviour.

Summary

Public Constructors
FieldMaskingSpanQuery(SpanQuery maskedQuery, String maskedField)
Public Methods
Weight createWeight(Searcher searcher)
Expert: Constructs an appropriate Weight implementation for this query.
boolean equals(Object o)
void extractTerms(Set<Term> terms)
Expert: adds all terms occurring in this query to the terms set.
String getField()
Returns the name of the field matched by this query.
SpanQuery getMaskedQuery()
Similarity getSimilarity(Searcher searcher)
This method is deprecated. Instead of using "runtime" subclassing/delegation, subclass the Weight instead.
Spans getSpans(IndexReader reader)
Expert: Returns the matches for this query in an index.
int hashCode()
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.
[Expand]
Inherited Methods
From class org.apache.lucene.search.spans.SpanQuery
From class org.apache.lucene.search.Query
From class java.lang.Object

Public Constructors

public FieldMaskingSpanQuery (SpanQuery maskedQuery, String maskedField)

Public Methods

public Weight createWeight (Searcher searcher)

Expert: Constructs an appropriate Weight implementation for this query.

Only implemented by primitive queries, which re-write to themselves.

Throws
IOException

public boolean equals (Object o)

public void extractTerms (Set<Term> terms)

Expert: adds all terms occurring in this query to the terms set. Only works if this query is in its rewritten form.

public String getField ()

Returns the name of the field matched by this query.

public SpanQuery getMaskedQuery ()

public Similarity getSimilarity (Searcher searcher)

This method is deprecated.
Instead of using "runtime" subclassing/delegation, subclass the Weight instead.

Expert: Returns the Similarity implementation to be used for this query. Subclasses may override this method to specify their own Similarity implementation, perhaps one that delegates through that of the Searcher. By default the Searcher's Similarity implementation is returned.

public Spans getSpans (IndexReader reader)

Expert: Returns the matches for this query in an index. Used internally to search for spans.

Throws
IOException

public int hashCode ()

public Query rewrite (IndexReader reader)

Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

Throws
IOException

public String toString (String field)

Prints a query to a string, with field assumed to be the default field and omitted.

The representation used is one that is supposed to be readable by QueryParser. However, there are the following limitations:

  • If the query was created by the parser, the printed representation may not be exactly what was parsed. For example, characters that need to be escaped will be represented without the required backslash.
  • Some of the more complicated queries (e.g. span queries) don't have a representation that can be parsed by QueryParser.