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Apache Solr (module: core)
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/*
 * 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.query;

import java.io.IOException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.ConstantScoreQuery;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.MatchNoDocsQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryVisitor;
import org.apache.lucene.search.ScoreMode;
import org.apache.lucene.search.Weight;
import org.apache.solr.search.DocSet;
import org.apache.solr.search.ExtendedQueryBase;
import org.apache.solr.search.SolrIndexSearcher;

/**
 * A filtered query wrapped around another query similar to {@link
 * org.apache.lucene.search.BooleanClause.Occur#FILTER} -- it scores as 0. Moreover, it will use
 * Solr's filter cache.
 */
public class FilterQuery extends ExtendedQueryBase {
  protected final Query q;

  public FilterQuery(Query q) {
    if (q == null) {
      this.q = new MatchNoDocsQuery();
      return;
    }
    this.q = q;
  }

  @Override
  public final void setCache(boolean cache) {
    /*
    NOTE: at the implementation level, we silently ignore explicit `setCache` directives. But at a higher level
    (i.e., from the client's perspective) by ignoring at the implementation level, we in fact respect the semantics
    both of explicit `{!cache=false}filter(q)` and `{!cache=true}filter(q)`. Since the purpose of FilterQuery
    is to handle caching _internal_ to the query, external `cache=false` _should_ have no effect. Slightly
    less intuitive: the `cache=true` case should be interpreted as directing "ensure that we consult the
    filterCache for this query" -- and indeed because caching is handled internally, the essence of the
    top-level `cache=true` directive is most appropriately respected by having `getCache()` continue to return
    `false` at the level of the FilterQuery _per se_.
     */
  }

  @Override
  public final boolean getCache() {
    return false;
    /*
    Paradoxically, this _is_ what we want. The FilterQuery wrapper is designed to ensure that its
    inner query always consults the filterCache, regardless of the context in which it's called.
    FilterQuery internally calls SolrIndexSearcher.getDocSet with its _wrapped_ query, so the caching
    happens at that level, and we want _not_ to consult the filterCache with the FilterQuery wrapper
    per se. Allowing `getCache()=true` here can result in double-entry in the filterCache (e.g. when
    using `fq=filter({!term f=field v=term})`, or caching separate clauses of a BooleanQuery via
    `fq={!bool should='filter($q1)' should='filter($q2)'}`).
     */
  }

  public Query getQuery() {
    return q;
  }

  @Override
  public int hashCode() {
    return q.hashCode() + 0xc0e65615;
  }

  @Override
  public boolean equals(Object obj) {
    if (!(obj instanceof FilterQuery)) return false;
    FilterQuery fq = (FilterQuery) obj;
    return this.q.equals(fq.q);
  }

  @Override
  public String toString(String field) {
    StringBuilder sb = new StringBuilder();
    sb.append("filter(");
    sb.append(q.toString(""));
    sb.append(')');
    return sb.toString();
  }

  @Override
  public void visit(QueryVisitor visitor) {
    q.visit(visitor.getSubVisitor(BooleanClause.Occur.FILTER, this));
  }

  @Override
  public Query rewrite(IndexReader reader) throws IOException {
    Query newQ = q.rewrite(reader);
    if (!newQ.equals(q)) {
      return new FilterQuery(newQ);
    } else {
      return this;
    }
  }

  @Override
  public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
      throws IOException {
    // SolrRequestInfo reqInfo = SolrRequestInfo.getRequestInfo();

    if (!(searcher instanceof SolrIndexSearcher)) {
      // delete-by-query won't have SolrIndexSearcher
      // note: CSQ has some optimizations so we wrap it even though unnecessary given 0 boost
      return new ConstantScoreQuery(q).createWeight(searcher, scoreMode, 0f);
    }

    SolrIndexSearcher solrSearcher = (SolrIndexSearcher) searcher;
    DocSet docs = solrSearcher.getDocSet(q);
    // reqInfo.addCloseHook(docs);  // needed for off-heap refcounting

    // note: DocSet.makeQuery is basically a CSQ
    return docs.makeQuery().createWeight(searcher, scoreMode, 0f);
  }
}