Package org.apache.lucene.search.spans

Class 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 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()

      • 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

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class Query