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

Modifier and Type	Method and Description
SpanWeight	createWeight(IndexSearcher searcher, boolean needsScores) Expert: Constructs an appropriate Weight implementation for this query.
boolean	equals(Object o)
String	getField() Returns the name of the field matched by this query.
SpanQuery	getMaskedQuery()
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.

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

getTermContexts, getTermContexts

Methods inherited from class org.apache.lucene.search.Query

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 o)

Overrides:

equals in class Query

hashCode

public int hashCode()

Overrides:

hashCode in class Query