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:

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

See Also:

Serialized Form

Constructor Summary

FieldMaskingSpanQuery(SpanQuery maskedQuery, String maskedField)

Method Summary

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()
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.

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

clone, combine, getBoost, getSimilarity, mergeBooleanQueries, setBoost, toString, weight

Methods inherited from class java.lang.Object

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()

getSpans

public Spans getSpans(IndexReader reader)
               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(Searcher 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.

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.

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