/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.queries.function.valuesource;
import java.io.IOException;
import java.util.Map;
import org.apache.lucene.index.AtomicReader;
import org.apache.lucene.index.AtomicReaderContext;
import org.apache.lucene.index.CompositeReader;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.ReaderUtil;
import org.apache.lucene.index.SlowCompositeReaderWrapper;
import org.apache.lucene.index.SortedDocValues;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.ValueSource;
import org.apache.lucene.queries.function.docvalues.IntDocValues;
import org.apache.lucene.search.FieldCache;
/**
* Obtains the ordinal of the field value from the default Lucene {@link org.apache.lucene.search.FieldCache} using getTermsIndex()
* and reverses the order.
* <br>
* The native lucene index order is used to assign an ordinal value for each field value.
* <br>Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
* <br>
* Example of reverse ordinal (rord):<br>
* If there were only three field values: "apple","banana","pear"
* <br>then rord("apple")=3, rord("banana")=2, ord("pear")=1
* <p>
* 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.
* <br>
* 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.
*
*
*/
public class ReverseOrdFieldSource extends ValueSource {
public final String field;
public ReverseOrdFieldSource(String field) {
this.field = field;
}
@Override
public String description() {
return "rord("+field+')';
}
// TODO: this is trappy? perhaps this query instead should make you pass a slow reader yourself?
@Override
public FunctionValues getValues(Map context, AtomicReaderContext readerContext) throws IOException {
final IndexReader topReader = ReaderUtil.getTopLevelContext(readerContext).reader();
final AtomicReader r = topReader instanceof CompositeReader
? new SlowCompositeReaderWrapper((CompositeReader)topReader)
: (AtomicReader) topReader;
final int off = readerContext.docBase;
final SortedDocValues sindex = FieldCache.DEFAULT.getTermsIndex(r, field);
final int end = sindex.getValueCount();
return new IntDocValues(this) {
@Override
public int intVal(int doc) {
return (end - sindex.getOrd(doc+off) - 1);
}
};
}
@Override
public boolean equals(Object o) {
if (o == null || (o.getClass() != ReverseOrdFieldSource.class)) return false;
ReverseOrdFieldSource other = (ReverseOrdFieldSource)o;
return this.field.equals(other.field);
}
private static final int hcode = ReverseOrdFieldSource.class.hashCode();
@Override
public int hashCode() {
return hcode + field.hashCode();
}
}