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From: bhupeshchawda <git@git.apache.org>
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References: <git-pr-282-apex-malhar@git.apache.org>
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Subject: [GitHub] apex-malhar pull request #282: APEXMALHAR-2066 JdbcPolling,idempotent,partit...
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Message-Id: <20160609002420.75718DFFAB@git1-us-west.apache.org>
Date: Thu,  9 Jun 2016 00:24:20 +0000 (UTC)
archived-at: Thu, 09 Jun 2016 00:24:26 -0000

Github user bhupeshchawda commented on a diff in the pull request:

    https://github.com/apache/apex-malhar/pull/282#discussion_r66365162
  
    --- Diff: library/src/main/java/com/datatorrent/lib/db/jdbc/JdbcMetaDataUtility.java ---
    @@ -0,0 +1,344 @@
    +/**
    + * 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 com.datatorrent.lib.db.jdbc;
    +
    +import java.sql.Connection;
    +import java.sql.DriverManager;
    +import java.sql.PreparedStatement;
    +import java.sql.ResultSet;
    +import java.sql.SQLException;
    +import java.util.HashMap;
    +
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
    +
    +import com.datatorrent.lib.util.KeyValPair;
    +
    +/**
    + * A utility class used to retrieve the metadata for a given unique key of a SQL
    + * table. This class would emit range queries based on a primary index given
    + * 
    + * @Input - dbName,tableName, primaryKey
    + * @Output - map<operatorId,prepared statement>
    + *
    + */
    +public class JdbcMetaDataUtility
    +{
    +  private static String DB_DRIVER = "com.mysql.jdbc.Driver";
    +  private static String DB_CONNECTION = "";
    +  private static String DB_USER = "";
    +  private static String DB_PASSWORD = "";
    +  private static String TABLE_NAME = "";
    +  private static String KEY_COLUMN = "";
    +  private static String WHERE_CLAUSE = null;
    +  private static String COLUMN_LIST = null;
    +
    +  private static Logger LOG = LoggerFactory.getLogger(JdbcMetaDataUtility.class);
    +
    +  public JdbcMetaDataUtility()
    +  {
    +
    +  }
    +
    +  public JdbcMetaDataUtility(String dbConnection, String tableName, String key, String userName, String password)
    +  {
    +    DB_CONNECTION = dbConnection;
    +    DB_USER = userName;
    +    DB_PASSWORD = password;
    +    TABLE_NAME = tableName;
    +    KEY_COLUMN = key;
    +  }
    +
    +  private static Connection getDBConnection()
    +  {
    +
    +    Connection dbConnection = null;
    +
    +    try {
    +      Class.forName(DB_DRIVER);
    +    } catch (ClassNotFoundException e) {
    +      LOG.error("Driver not found", e);
    +    }
    +
    +    try {
    +      dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER, DB_PASSWORD);
    +      return dbConnection;
    +    } catch (SQLException e) {
    +      LOG.error("Exception in getting connection handle", e);
    +    }
    +
    +    return dbConnection;
    +
    +  }
    +
    +  private static String generateQueryString()
    +  {
    +    StringBuilder sb = new StringBuilder();
    +    sb.append("SELECT COUNT(*) as RowCount from " + TABLE_NAME);
    +
    +    if (WHERE_CLAUSE != null) {
    +      sb.append(" WHERE " + WHERE_CLAUSE);
    +    }
    +
    +    return sb.toString();
    +  }
    +
    +  /**
    +   * Finds the total number of rows in the table
    +   */
    +  private static long getRecordRange(String query) throws SQLException
    +  {
    +    long rowCount = 0;
    +    Connection dbConnection = null;
    +    PreparedStatement preparedStatement = null;
    +
    +    try {
    +      dbConnection = getDBConnection();
    +      preparedStatement = dbConnection.prepareStatement(query);
    +
    +      ResultSet rs = preparedStatement.executeQuery();
    +
    +      while (rs.next()) {
    +        rowCount = Long.parseLong(rs.getString("RowCount"));
    +        LOG.info("# Rows - " + rowCount);
    +      }
    +
    +    } catch (SQLException e) {
    +      LOG.error("Exception in retreiving result set", e);
    +    } finally {
    +      if (preparedStatement != null) {
    +        preparedStatement.close();
    +      }
    +      if (dbConnection != null) {
    +        dbConnection.close();
    +      }
    +    }
    +    return rowCount;
    +  }
    +
    +  /**
    +   * Returns a pair of <upper,lower> bounds for each partition of the
    +   * {@link JdbcPollInputOperator}}
    +   */
    +  private static KeyValPair<String, String> getQueryBounds(long lower, long upper) throws SQLException
    +  {
    +    Connection dbConnectionLower = null;
    +    Connection dbConnectionUpper = null;
    +    PreparedStatement psLowerBound = null;
    +    PreparedStatement psUpperBound = null;
    +
    +    StringBuilder lowerBound = new StringBuilder();
    +    StringBuilder upperBound = new StringBuilder();
    +
    +    KeyValPair<String, String> boundedQUeryPair = null;
    +
    +    try {
    +      dbConnectionLower = getDBConnection();
    +      dbConnectionUpper = getDBConnection();
    +
    +      /*
    +       * Run this loop only for n-1 partitions.
    +       * By default the last partition will have fewer records, since we are rounding off
    +       * */
    +
    +      lowerBound.append("SELECT " + KEY_COLUMN + " FROM " + TABLE_NAME);
    +      upperBound.append("SELECT " + KEY_COLUMN + " FROM " + TABLE_NAME);
    +
    +      if (WHERE_CLAUSE != null) {
    +        lowerBound.append(" WHERE " + WHERE_CLAUSE);
    +        upperBound.append(" WHERE " + WHERE_CLAUSE);
    +      }
    +
    +      lowerBound.append(" LIMIT " + (0 + lower) + ",1");
    --- End diff --
    
    LIMIT clause might not work with all databases. Need to document this.


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