package org.apache.lucene.search.grouping;
/**
* 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.
*/
import java.io.IOException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.search.Sort;
/**
* Concrete implementation of {@link AbstractFirstPassGroupingCollector} that groups based on
* field values and more specifically uses {@link org.apache.lucene.search.FieldCache.StringIndex}
* to collect groups.
*
* @lucene.experimental
*/
public class TermFirstPassGroupingCollector extends AbstractFirstPassGroupingCollector<String> {
private FieldCache.StringIndex index;
private String groupField;
/**
* Create the first pass collector.
*
* @param groupField The field used to group
* documents. This field must be single-valued and
* indexed (FieldCache is used to access its value
* per-document).
* @param groupSort The {@link Sort} used to sort the
* groups. The top sorted document within each group
* according to groupSort, determines how that group
* sorts against other groups. This must be non-null,
* ie, if you want to groupSort by relevance use
* Sort.RELEVANCE.
* @param topNGroups How many top groups to keep.
* @throws IOException When I/O related errors occur
*/
public TermFirstPassGroupingCollector(String groupField, Sort groupSort, int topNGroups) throws IOException {
super(groupSort, topNGroups);
this.groupField = groupField;
}
@Override
protected String getDocGroupValue(int doc) {
final int ord = index.order[doc];
return ord == 0 ? null : index.lookup[ord];
}
@Override
protected String copyDocGroupValue(String groupValue, String reuse) {
return groupValue;
}
@Override
public void setNextReader(IndexReader reader, int docBase) throws IOException {
super.setNextReader(reader, docBase);
index = FieldCache.DEFAULT.getStringIndex(reader, groupField);
}
}