001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.mapreduce.lib.db;
019
020import java.sql.PreparedStatement;
021import java.sql.ResultSet;
022import java.sql.SQLException;
023
024import org.apache.hadoop.classification.InterfaceAudience;
025import org.apache.hadoop.classification.InterfaceStability;
026import org.apache.hadoop.io.Writable;
027
028/**
029 * Objects that are read from/written to a database should implement
030 * <code>DBWritable</code>. DBWritable, is similar to {@link Writable} 
031 * except that the {@link #write(PreparedStatement)} method takes a 
032 * {@link PreparedStatement}, and {@link #readFields(ResultSet)} 
033 * takes a {@link ResultSet}. 
034 * <p>
035 * Implementations are responsible for writing the fields of the object 
036 * to PreparedStatement, and reading the fields of the object from the 
037 * ResultSet. 
038 * 
039 * <p>Example:</p>
040 * If we have the following table in the database :
041 * <pre>
042 * CREATE TABLE MyTable (
043 *   counter        INTEGER NOT NULL,
044 *   timestamp      BIGINT  NOT NULL,
045 * );
046 * </pre>
047 * then we can read/write the tuples from/to the table with :
048 * <p><pre>
049 * public class MyWritable implements Writable, DBWritable {
050 *   // Some data     
051 *   private int counter;
052 *   private long timestamp;
053 *       
054 *   //Writable#write() implementation
055 *   public void write(DataOutput out) throws IOException {
056 *     out.writeInt(counter);
057 *     out.writeLong(timestamp);
058 *   }
059 *       
060 *   //Writable#readFields() implementation
061 *   public void readFields(DataInput in) throws IOException {
062 *     counter = in.readInt();
063 *     timestamp = in.readLong();
064 *   }
065 *       
066 *   public void write(PreparedStatement statement) throws SQLException {
067 *     statement.setInt(1, counter);
068 *     statement.setLong(2, timestamp);
069 *   }
070 *       
071 *   public void readFields(ResultSet resultSet) throws SQLException {
072 *     counter = resultSet.getInt(1);
073 *     timestamp = resultSet.getLong(2);
074 *   } 
075 * }
076 * </pre></p>
077 */
078@InterfaceAudience.Public
079@InterfaceStability.Stable
080public interface DBWritable {
081
082  /**
083   * Sets the fields of the object in the {@link PreparedStatement}.
084   * @param statement the statement that the fields are put into.
085   * @throws SQLException
086   */
087        public void write(PreparedStatement statement) throws SQLException;
088        
089        /**
090         * Reads the fields of the object from the {@link ResultSet}. 
091         * @param resultSet the {@link ResultSet} to get the fields from.
092         * @throws SQLException
093         */
094        public void readFields(ResultSet resultSet) throws SQLException ; 
095}