ReverseOrdFieldSource

Class Overview

Expert: obtains the ordinal of the field value from the default Lucene FieldCache using getStringIndex() 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: rord() 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: The status of the search.function package is experimental. The APIs introduced here might change in the future and will not be supported anymore in such a case.

NOTE: with the switch in 2.9 to segment-based searching, if getValues(IndexReader) is invoked with a composite (multi-segment) reader, this can easily cause double RAM usage for the values in the FieldCache. It's best to switch your application to pass only atomic (single segment) readers to this API.

Summary

[Expand] Inherited Methods
From class org.apache.lucene.search.function.ValueSource abstract String description() description of field, used in explain() abstract boolean equals(Object o) Needed for possible caching of query results - used by equals(Object). abstract DocValues getValues(IndexReader reader) Return the DocValues used by the function query. abstract int hashCode() Needed for possible caching of query results - used by hashCode(). String toString()
From class java.lang.Object Object clone() boolean equals(Object arg0) void finalize() final Class<?> getClass() int hashCode() final void notify() final void notifyAll() String toString() final void wait() final void wait(long arg0, int arg1) final void wait(long arg0)