solr/core/src/java/org/apache/solr/search/PostFilter.java

/*
 * 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.solr.search;

import org.apache.lucene.search.IndexSearcher;

/** The PostFilter interface provides a mechanism to further filter documents
 * after they have already gone through the main query and other filters.
 * This is appropriate for filters with a very high cost.
 * <p>
 * The filtering mechanism used is a {@link DelegatingCollector}
 * that allows the filter to not call the delegate for certain documents,
 * thus effectively filtering them out.  This also avoids the normal
 * filter advancing mechanism which asks for the first acceptable document on
 * or after the target (which is undesirable for expensive filters).
 * This collector interface also enables better performance when an external system
 * must be consulted, since document ids may be buffered and batched into
 * a single request to the external system.
 * <p>
 * Implementations of this interface must also be a Query.
 * If an implementation can only support the collector method of
 * filtering through getFilterCollector, then ExtendedQuery.getCached()
 * should always return false, and ExtendedQuery.getCost() should
 * return no less than 100.
 *
 * @see ExtendedQueryBase
 */
public interface PostFilter extends ExtendedQuery {

  /** Returns a DelegatingCollector to be run after the main query and all of its filters, but before any sorting or grouping collectors */
  public DelegatingCollector getFilterCollector(IndexSearcher searcher);
}