Package org.apache.lucene.search.spans

Class 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 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,
                               ScoreMode scoreMode,
                               float boost)
                        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
        scoreMode - How the produced scorers will be consumed.
        boost - The boost that is propagated by the parent queries.
        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

      • visit

        public void visit​(QueryVisitor visitor)
        Description copied from class: Query
        Recurse through the query tree, visiting any child queries
        Overrides:
        visit in class Query
        Parameters:
        visitor - a QueryVisitor to be called by each query in the tree

      • 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 other)
        Description copied from class: Query
        Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly. Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.
        Specified by:
        equals in class Query
        See Also:
        Query.sameClassAs(Object), Query.classHash()

      • hashCode

        public int hashCode()
        Description copied from class: Query
        Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.
        Specified by:
        hashCode in class Query
        See Also:
        Query.equals(Object)