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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.update.processor;

import static org.apache.solr.update.processor.FieldMutatingUpdateProcessor.SELECT_NO_FIELDS;

import java.util.Collection;
import java.util.Collections;
import org.apache.solr.core.SolrCore;
import org.apache.solr.update.processor.FieldMutatingUpdateProcessor.FieldNameSelector;

/**
 * Keeps only the first value of fields matching the specified conditions. Correct behavior assumes
 * that the SolrInputFields being mutated are either single valued, or use an ordered Collection
 * (ie: not a Set).
 *
 * By default, this processor matches no fields.
 *
 * 
For example, in the configuration below, if a field named primary_author
 * contained multiple values (ie: "Adam Doe", "Bob Smith", "Carla Jones") then only the
 * first value (ie: "Adam Doe") will be kept
 *
 * 
 * <processor class="solr.FirstFieldValueUpdateProcessorFactory">
 *   <str name="fieldName">primary_author</str>
 * </processor>
 * 
 *
 * @see LastFieldValueUpdateProcessorFactory
 * @since 4.0.0
 */
public final class FirstFieldValueUpdateProcessorFactory
    extends FieldValueSubsetUpdateProcessorFactory {

  @Override
  public  Collection pickSubset(Collection values) {
    // trust the iterator
    return Collections.singletonList(values.iterator().next());
  }

  @Override
  public FieldNameSelector getDefaultSelector(SolrCore core) {
    return SELECT_NO_FIELDS;
  }
}