package org.apache.lucene.search;
/*
* 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.AtomicReader; // javadocs
import org.apache.lucene.index.AtomicReaderContext;
import org.apache.lucene.util.Bits;
/**
* Abstract base class for restricting which documents may
* be returned during searching.
*/
public abstract class Filter {
/**
* Creates a {@link DocIdSet} enumerating the documents that should be
* permitted in search results. <b>NOTE:</b> null can be
* returned if no documents are accepted by this Filter.
* <p>
* Note: This method will be called once per segment in
* the index during searching. The returned {@link DocIdSet}
* must refer to document IDs for that segment, not for
* the top-level reader.
*
* @param context a {@link AtomicReaderContext} instance opened on the index currently
* searched on. Note, it is likely that the provided reader info does not
* represent the whole underlying index i.e. if the index has more than
* one segment the given reader only represents a single segment.
* The provided context is always an atomic context, so you can call
* {@link AtomicReader#fields()}
* on the context's reader, for example.
*
* @param acceptDocs
* Bits that represent the allowable docs to match (typically deleted docs
* but possibly filtering other documents)
*
* @return a DocIdSet that provides the documents which should be permitted or
* prohibited in search results. <b>NOTE:</b> <code>null</code> should be returned if
* the filter doesn't accept any documents otherwise internal optimization might not apply
* in the case an <i>empty</i> {@link DocIdSet} is returned.
*/
public abstract DocIdSet getDocIdSet(AtomicReaderContext context, Bits acceptDocs) throws IOException;
}