external/storm-jdbc/src/main/java/org/apache/storm/jdbc/mapper/JdbcLookupMapper.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.storm.jdbc.mapper;

import java.util.List;
import org.apache.storm.jdbc.common.Column;
import org.apache.storm.topology.OutputFieldsDeclarer;
import org.apache.storm.tuple.ITuple;
import org.apache.storm.tuple.Values;

public interface JdbcLookupMapper extends JdbcMapper {

    /**
     * Converts a DB row to a list of storm values that can be emitted. This is done to allow a single
     * storm input tuple and a single DB row to result in multiple output values.
     * @param input the input tuple.
     * @param columns list of columns that represents a row
     * @return a List of storm values that can be emitted. Each item in list is emitted as an output tuple.
     */
    List<Values> toTuple(ITuple input, List<Column> columns);

    /**
     * declare what are the fields that this code will output.
     */
    void declareOutputFields(OutputFieldsDeclarer declarer);
}