Metacat

/**

 *  '$RCSfile$'

 *    Purpose: An abstract class that encapsulates access to any RDBMS.

 *             This allows to swap easily between databases without any

 *             modification to the application.

 *  Copyright: 2000 Regents of the University of California and the

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Jivka Bojilova

 *

 *   '$Author: daigle $'

 *     '$Date: 2009-08-24 14:34:17 -0700 (Mon, 24 Aug 2009) $'

 * '$Revision: 5030 $'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.dbadapter;

import java.sql.*;

import edu.ucsb.nceas.metacat.properties.PropertyService;

/**

 * Java offers uniform database access through the use of JDBC.

 * But many databases still use different SQL implementations and 

 * conventions. Thus this class offers extended programming interface

 * that all subclasses should implement to gain access to different

 * databases.

 *

 * To add a new database adapter class you must create a new class 

 * <dbname>Adapter that extends edu.ucsb.nceas.dbadapter.AbstarctDatabase

 * (where dbname is the name of the database or database driver you wish

 * to add to your application). AbstarctDatabase is an abstract class,

 * thus the subclasses need to implement the abstract methods.

 */

public abstract class AbstractDatabase {

  /**

   * Unique ID generator

   *

   * @param conn db connection in which the unique id was generated

   * @param tableName the table which unique id was generate

   * @exception SQLException <br/> any SQLException that can be thrown 

   *            during the db operation

   * @return return the generated unique id as a long type

   */

  public abstract long getUniqueID(Connection conn, String tableName) 

                                                  throws SQLException;

  /**

   * The function name that gets the current date and time

   * from the database server

   *

   * @return return the current date and time function name

   */

  public abstract String getDateTimeFunction();

  /**

   * The function name that is used to return non-NULL value

   *

   * @return return the non-NULL function name

   */

  public abstract String getIsNULLFunction();

  /**

   * The character that the specific database implementation uses to 

   * indicate string literals in SQL. This will usually be a single

   * qoute (').

   *

   * @return return the string delimiter

   */

  public abstract String getStringDelimiter();

  /**

   * MSSQL didn't support to_date function which to transfer a text string

   * to date type. But Oracle and Postsql do.

   */

  public String toDate(String dateString, String format)

  {

    return "to_date(" + "'"+ dateString + "', '" + format + "')";

  }

  /**

   * Syntax for doing a left join

   * Add 'a.' in front of the fields for first table and

   * 'b.' in front of the fields for the second table

   * 

   * @param selectFields fields that you want to be selected

   * @param tableA first table in the join

   * @param tableB second table in the join

   * @param joinCriteria the criteria based on which the join will be made

   * @param nonJoinCriteria all other criterias

   * @return return the string for teh select query

   */

  public abstract String getLeftJoinQuery(String selectFields, String tableA, 

		  String tableB, String joinCriteria, String nonJoinCriteria);

  /**

   * Instantiate a class using the name of the class at runtime

   *

   * @param className the fully qualified name of the class to instantiate

   */

  static public Object createObject(String className) throws Exception {

    Object object = null;

    try {

      Class classDefinition = Class.forName(className);

      object = classDefinition.newInstance();

    } catch (InstantiationException e) {

      throw e;

    } catch (IllegalAccessException e) {

      throw e;

    } catch (ClassNotFoundException e) {

      throw e;

    }

    return object;

  }

  /**

   * the main routine used to test the dbadapter utility.

   */

  static public void main(String[] args) {

    // Determine our db adapter class and

    // create an instance of that class

    try {

      String dbAdapter = PropertyService.getProperty("database.adapter");

      AbstractDatabase dbAdapterObj = (AbstractDatabase)createObject(dbAdapter);

      // test if they work correctly

      String date = dbAdapterObj.getDateTimeFunction();

    } catch (Exception e) {

      System.out.println(e);

    }

  }

  /**

   * This method will return the sql command to get document list in xml_document

   * in replication. Because it involes outer join, so this method is very flexible.

   * @return

   */

  public abstract String getReplicationDocumentListSQL();

}