Package org.apache.lucene.queries.function.valuesource

Class ReverseOrdFieldSource

java.lang.Object
org.apache.lucene.queries.function.ValueSource
org.apache.lucene.queries.function.valuesource.ReverseOrdFieldSource
public class ReverseOrdFieldSource extends ValueSource
Obtains the ordinal of the field value from the default Lucene FieldCache using getTermsIndex() and reverses the order.
The native lucene index order is used to assign an ordinal value for each field value.
Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
Example of reverse ordinal (rord):
If there were only three field values: "apple","banana","pear"
then rord("apple")=3, rord("banana")=2, ord("pear")=1

WARNING: ord() depends on the position in an index and can thus change when other documents are inserted or deleted, or if a MultiSearcher is used.
WARNING: as of Solr 1.4, ord() and rord() can cause excess memory use since they must use a FieldCache entry at the top level reader, while sorting and function queries now use entries at the segment level. Hence sorting or using a different function query, in addition to ord()/rord() will double memory use.