/*
 *    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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 *    DatabaseUtils.java
 *    Copyright (C) 1999 University of Waikato, Hamilton, New Zealand
 *
 */

package weka.experiment;

import java.io.Serializable;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Types;
import java.util.Collections;
import java.util.HashSet;
import java.util.Properties;
import java.util.StringTokenizer;
import java.util.Vector;

import weka.core.RevisionHandler;
import weka.core.RevisionUtils;
import weka.core.Utils;

/**
 * DatabaseUtils provides utility functions for accessing the experiment
 * database. The jdbc driver and database to be used default to "jdbc.idbDriver"
 * and "jdbc:idb=experiments.prp". These may be changed by creating a java
 * properties file called DatabaseUtils.props in user.home or the current
 * directory. eg:
 * <p>
 * 
 * <code><pre>
 * jdbcDriver=jdbc.idbDriver
 * jdbcURL=jdbc:idb=experiments.prp
 * </pre></code>
 * <p>
 * 
 * @author Len Trigg (trigg@cs.waikato.ac.nz)
 * @version $Revision: 11887 $
 */
public class DatabaseUtils implements Serializable, RevisionHandler {

  /** for serialization. */
  static final long serialVersionUID = -8252351994547116729L;

  /** The name of the table containing the index to experiments. */
  public static final String EXP_INDEX_TABLE = "Experiment_index";

  /** The name of the column containing the experiment type (ResultProducer). */
  public static final String EXP_TYPE_COL = "Experiment_type";

  /** The name of the column containing the experiment setup (parameters). */
  public static final String EXP_SETUP_COL = "Experiment_setup";

  /** The name of the column containing the results table name. */
  public static final String EXP_RESULT_COL = "Result_table";

  /** The prefix for result table names. */
  public static final String EXP_RESULT_PREFIX = "Results";

  /** The name of the properties file. */
  public final static String PROPERTY_FILE = "weka/experiment/DatabaseUtils.props";

  /** Holds the jdbc drivers to be used (only to stop them being gc'ed). */
  protected Vector DRIVERS = new Vector();

  /** keeping track of drivers that couldn't be loaded. */
  protected static Vector DRIVERS_ERRORS;

  /** Properties associated with the database connection. */
  protected Properties PROPERTIES;

  /* Type mapping used for reading experiment results */
  /** Type mapping for STRING used for reading experiment results. */
  public static final int STRING = 0;
  /** Type mapping for BOOL used for reading experiment results. */
  public static final int BOOL = 1;
  /** Type mapping for DOUBLE used for reading experiment results. */
  public static final int DOUBLE = 2;
  /** Type mapping for BYTE used for reading experiment results. */
  public static final int BYTE = 3;
  /** Type mapping for SHORT used for reading experiment results. */
  public static final int SHORT = 4;
  /** Type mapping for INTEGER used for reading experiment results. */
  public static final int INTEGER = 5;
  /** Type mapping for LONG used for reading experiment results. */
  public static final int LONG = 6;
  /** Type mapping for FLOAT used for reading experiment results. */
  public static final int FLOAT = 7;
  /** Type mapping for DATE used for reading experiment results. */
  public static final int DATE = 8;
  /** Type mapping for TEXT used for reading, e.g., text blobs. */
  public static final int TEXT = 9;
  /** Type mapping for TIME used for reading TIME columns. */
  public static final int TIME = 10;
  /** Type mapping for TIMESTAMP used for reading java.sql.Timestamp columns */
  public static final int TIMESTAMP = 11;

  /** Database URL. */
  protected String m_DatabaseURL;

  /** The prepared statement used for database queries. */
  protected transient PreparedStatement m_PreparedStatement;

  /** The database connection. */
  protected transient Connection m_Connection;

  /** True if debugging output should be printed. */
  protected boolean m_Debug = false;

  /** Database username. */
  protected String m_userName = "";

  /** Database Password. */
  protected String m_password = "";

  /* mappings used for creating Tables. Can be overridden in DatabaseUtils.props */
  /** string type for the create table statement. */
  protected String m_stringType = "LONGVARCHAR";
  /** integer type for the create table statement. */
  protected String m_intType = "INT";
  /** double type for the create table statement. */
  protected String m_doubleType = "DOUBLE";

  /** For databases where Tables and Columns are created in upper case. */
  protected boolean m_checkForUpperCaseNames = false;

  /** For databases where Tables and Columns are created in lower case. */
  protected boolean m_checkForLowerCaseNames = false;

  /** setAutoCommit on the database? */
  protected boolean m_setAutoCommit = true;

  /** create index on the database? */
  protected boolean m_createIndex = false;

  /** the keywords for the current database type. */
  protected HashSet<String> m_Keywords = new HashSet<String>();

  /** the character to mask SQL keywords (by appending this character). */
  protected String m_KeywordsMaskChar = "_";

  /**
   * Reads properties and sets up the database drivers.
   * 
   * @throws Exception if an error occurs
   */
  public DatabaseUtils() throws Exception {
    if (DRIVERS_ERRORS == null) {
      DRIVERS_ERRORS = new Vector();
    }

    try {
      PROPERTIES = Utils.readProperties(PROPERTY_FILE);

      // Register the drivers in jdbc DriverManager
      String drivers = PROPERTIES.getProperty("jdbcDriver", "jdbc.idbDriver");

      if (drivers == null) {
        throw new Exception("No database drivers (JDBC) specified");
      }
      // The call to newInstance() is necessary on some platforms
      // (with some java VM implementations)
      StringTokenizer st = new StringTokenizer(drivers, ", ");
      while (st.hasMoreTokens()) {
        String driver = st.nextToken();
        boolean result;
        try {
          Class.forName(driver);
          DRIVERS.addElement(driver);
          result = true;
        } catch (Exception e) {
          result = false;
        }
        if (m_Debug || (!result && !DRIVERS_ERRORS.contains(driver))) {
          System.err.println("Trying to add database driver (JDBC): " + driver
            + " - " + (result ? "Success!" : "Error, not in CLASSPATH?"));
        }
        if (!result) {
          DRIVERS_ERRORS.add(driver);
        }
      }
    } catch (Exception ex) {
      System.err.println("Problem reading properties. Fix before continuing.");
      System.err.println(ex);
    }

    m_DatabaseURL = PROPERTIES.getProperty("jdbcURL",
      "jdbc:idb=experiments.prp");
    m_stringType = PROPERTIES.getProperty("CREATE_STRING", "LONGVARCHAR");
    m_intType = PROPERTIES.getProperty("CREATE_INT", "INT");
    m_doubleType = PROPERTIES.getProperty("CREATE_DOUBLE", "DOUBLE");
    m_checkForUpperCaseNames = PROPERTIES.getProperty("checkUpperCaseNames",
      "false").equals("true");
    m_checkForLowerCaseNames = PROPERTIES.getProperty("checkLowerCaseNames",
      "false").equals("true");
    m_setAutoCommit = PROPERTIES.getProperty("setAutoCommit", "true").equals(
      "true");
    m_createIndex = PROPERTIES.getProperty("createIndex", "false").equals(
      "true");
    setKeywords(PROPERTIES.getProperty("Keywords",
      "AND,ASC,BY,DESC,FROM,GROUP,INSERT,ORDER,SELECT,UPDATE,WHERE"));
    setKeywordsMaskChar(PROPERTIES.getProperty("KeywordsMaskChar", "_"));
  }

  /**
   * returns key column headings in their original case. Used for those
   * databases that create uppercase column names.
   * 
   * @param columnName the column to retrieve the original case for
   * @return the original case
   */
  protected String attributeCaseFix(String columnName) {
    if (m_checkForUpperCaseNames) {
      String ucname = columnName.toUpperCase();
      if (ucname.equals(EXP_TYPE_COL.toUpperCase())) {
        return EXP_TYPE_COL;
      } else if (ucname.equals(EXP_SETUP_COL.toUpperCase())) {
        return EXP_SETUP_COL;
      } else if (ucname.equals(EXP_RESULT_COL.toUpperCase())) {
        return EXP_RESULT_COL;
      } else {
        return columnName;
      }
    } else if (m_checkForLowerCaseNames) {
      String ucname = columnName.toLowerCase();
      if (ucname.equals(EXP_TYPE_COL.toLowerCase())) {
        return EXP_TYPE_COL;
      } else if (ucname.equals(EXP_SETUP_COL.toLowerCase())) {
        return EXP_SETUP_COL;
      } else if (ucname.equals(EXP_RESULT_COL.toLowerCase())) {
        return EXP_RESULT_COL;
      } else {
        return columnName;
      }
    } else {
      return columnName;
    }
  }

  /**
   * translates the column data type string to an integer value that indicates
   * which data type / get()-Method to use in order to retrieve values from the
   * database (see DatabaseUtils.Properties, InstanceQuery()). Blanks in the
   * type are replaced with underscores "_", since Java property names can't
   * contain blanks.
   * 
   * @param type the column type as retrieved with
   *          java.sql.MetaData.getColumnTypeName(int)
   * @return an integer value that indicates which data type / get()-Method to
   *         use in order to retrieve values from the
   */
  public int translateDBColumnType(String type) {
    try {
      // Oracle, e.g., has datatypes like "DOUBLE PRECISION"
      // BUT property names can't have blanks in the name (unless escaped with
      // a backslash), hence also check for names where the blanks are
      // replaced with underscores "_":
      String value = PROPERTIES.getProperty(type);
      String typeUnderscore = type.replaceAll(" ", "_");
      if (value == null) {
        value = PROPERTIES.getProperty(typeUnderscore);
      }
      return Integer.parseInt(value);
    } catch (NumberFormatException e) {
      throw new IllegalArgumentException("Unknown data type: " + type + ". "
        + "Add entry in " + PROPERTY_FILE + ".\n"
        + "If the type contains blanks, either escape them with a backslash "
        + "or use underscores instead of blanks.");
    }
  }

  /**
   * Converts an array of objects to a string by inserting a space between each
   * element. Null elements are printed as ?
   * 
   * @param array the array of objects
   * @return a value of type 'String'
   */
  public static String arrayToString(Object[] array) {
    String result = "";
    if (array == null) {
      result = "<null>";
    } else {
      for (Object element : array) {
        if (element == null) {
          result += " ?";
        } else {
          result += " " + element;
        }
      }
    }
    return result;
  }

  /**
   * Returns the name associated with a SQL type.
   * 
   * @param type the SQL type
   * @return the name of the type
   */
  public static String typeName(int type) {
    switch (type) {
    case Types.BIGINT:
      return "BIGINT ";
    case Types.BINARY:
      return "BINARY";
    case Types.BIT:
      return "BIT";
    case Types.CHAR:
      return "CHAR";
    case Types.DATE:
      return "DATE";
    case Types.DECIMAL:
      return "DECIMAL";
    case Types.DOUBLE:
      return "DOUBLE";
    case Types.FLOAT:
      return "FLOAT";
    case Types.INTEGER:
      return "INTEGER";
    case Types.LONGVARBINARY:
      return "LONGVARBINARY";
    case Types.LONGVARCHAR:
      return "LONGVARCHAR";
    case Types.NULL:
      return "NULL";
    case Types.NUMERIC:
      return "NUMERIC";
    case Types.OTHER:
      return "OTHER";
    case Types.REAL:
      return "REAL";
    case Types.SMALLINT:
      return "SMALLINT";
    case Types.TIME:
      return "TIME";
    case Types.TIMESTAMP:
      return "TIMESTAMP";
    case Types.TINYINT:
      return "TINYINT";
    case Types.VARBINARY:
      return "VARBINARY";
    case Types.VARCHAR:
      return "VARCHAR";
    default:
      return "Unknown";
    }
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String databaseURLTipText() {
    return "Set the URL to the database.";
  }

  /**
   * Get the value of DatabaseURL.
   * 
   * @return Value of DatabaseURL.
   */
  public String getDatabaseURL() {
    return m_DatabaseURL;
  }

  /**
   * Set the value of DatabaseURL.
   * 
   * @param newDatabaseURL Value to assign to DatabaseURL.
   */
  public void setDatabaseURL(String newDatabaseURL) {
    m_DatabaseURL = newDatabaseURL;
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String debugTipText() {
    return "Whether debug information is printed.";
  }

  /**
   * Sets whether there should be printed some debugging output to stderr or
   * not.
   * 
   * @param d true if output should be printed
   */
  public void setDebug(boolean d) {
    m_Debug = d;
  }

  /**
   * Gets whether there should be printed some debugging output to stderr or
   * not.
   * 
   * @return true if output should be printed
   */
  public boolean getDebug() {
    return m_Debug;
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String usernameTipText() {
    return "The user to use for connecting to the database.";
  }

  /**
   * Set the database username.
   * 
   * @param username Username for Database.
   */
  public void setUsername(String username) {
    m_userName = username;
  }

  /**
   * Get the database username.
   * 
   * @return Database username
   */
  public String getUsername() {
    return m_userName;
  }

  /**
   * Returns the tip text for this property.
   * 
   * @return tip text for this property suitable for displaying in the
   *         explorer/experimenter gui
   */
  public String passwordTipText() {
    return "The password to use for connecting to the database.";
  }

  /**
   * Set the database password.
   * 
   * @param password Password for Database.
   */
  public void setPassword(String password) {
    m_password = password;
  }

  /**
   * Get the database password.
   * 
   * @return Password for Database.
   */
  public String getPassword() {
    return m_password;
  }

  /**
   * Opens a connection to the database.
   * 
   * @throws Exception if an error occurs
   */
  public void connectToDatabase() throws Exception {
    if (m_Debug) {
      System.err.println("Connecting to " + m_DatabaseURL);
    }
    if (m_Connection == null) {
      if (m_userName.equals("")) {
        try {
          m_Connection = DriverManager.getConnection(m_DatabaseURL);
        } catch (java.sql.SQLException e) {

          // Try loading the drivers
          for (int i = 0; i < DRIVERS.size(); i++) {
            try {
              Class.forName((String) DRIVERS.elementAt(i));
            } catch (Exception ex) {
              // Drop through
            }
          }
          m_Connection = DriverManager.getConnection(m_DatabaseURL);
        }
      } else {
        try {
          m_Connection = DriverManager.getConnection(m_DatabaseURL, m_userName,
            m_password);
        } catch (java.sql.SQLException e) {

          // Try loading the drivers
          for (int i = 0; i < DRIVERS.size(); i++) {
            try {
              Class.forName((String) DRIVERS.elementAt(i));
            } catch (Exception ex) {
              // Drop through
            }
          }
          m_Connection = DriverManager.getConnection(m_DatabaseURL, m_userName,
            m_password);
        }
      }
    }
    m_Connection.setAutoCommit(m_setAutoCommit);
  }

  /**
   * Closes the connection to the database.
   * 
   * @throws Exception if an error occurs
   */
  public void disconnectFromDatabase() throws Exception {
    if (m_Debug) {
      System.err.println("Disconnecting from " + m_DatabaseURL);
    }
    if (m_Connection != null) {
      m_Connection.close();
      m_Connection = null;
    }
  }

  /**
   * Returns true if a database connection is active.
   * 
   * @return a value of type 'boolean'
   */
  public boolean isConnected() {
    return (m_Connection != null);
  }

  /**
   * Returns whether the cursors only support forward movement or are scroll
   * sensitive (with ResultSet.CONCUR_READ_ONLY concurrency). Returns always
   * false if not connected
   * 
   * @return true if connected and the cursor is scroll-sensitive
   * @see ResultSet#TYPE_SCROLL_SENSITIVE
   * @see ResultSet#TYPE_FORWARD_ONLY
   * @see ResultSet#CONCUR_READ_ONLY
   */
  public boolean isCursorScrollSensitive() {
    boolean result;

    result = false;

    try {
      if (isConnected()) {
        result = m_Connection.getMetaData().supportsResultSetConcurrency(
          ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
      }
    } catch (Exception e) {
      // ignored
    }

    return result;
  }

  /**
   * Checks whether cursors are scrollable in general, false otherwise (also if
   * not connected).
   * 
   * @return true if scrollable and connected
   * @see #getSupportedCursorScrollType()
   */
  public boolean isCursorScrollable() {
    return (getSupportedCursorScrollType() != -1);
  }

  /**
   * Returns the type of scrolling that the cursor supports, -1 if not supported
   * or not connected. Checks first for TYPE_SCROLL_SENSITIVE and then for
   * TYPE_SCROLL_INSENSITIVE. In both cases CONCUR_READ_ONLY as concurrency is
   * used.
   * 
   * @return the scroll type, or -1 if not connected or no scrolling supported
   * @see ResultSet#TYPE_SCROLL_SENSITIVE
   * @see ResultSet#TYPE_SCROLL_INSENSITIVE
   */
  public int getSupportedCursorScrollType() {
    int result;

    result = -1;

    try {
      if (isConnected()) {
        if (m_Connection.getMetaData().supportsResultSetConcurrency(
          ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY)) {
          result = ResultSet.TYPE_SCROLL_SENSITIVE;
        }

        if (result == -1) {
          if (m_Connection.getMetaData().supportsResultSetConcurrency(
            ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY)) {
            result = ResultSet.TYPE_SCROLL_INSENSITIVE;
          }
        }
      }
    } catch (Exception e) {
      // ignored
    }

    return result;
  }

  /**
   * Executes a SQL query. Caller must clean up manually with
   * <code>close()</code>.
   * 
   * @param query the SQL query
   * @return true if the query generated results
   * @throws SQLException if an error occurs
   * @see #close()
   */
  public boolean execute(String query) throws SQLException {
    if (!isConnected()) {
      throw new IllegalStateException("Not connected, please connect first!");
    }

    if (!isCursorScrollable()) {
      m_PreparedStatement = m_Connection.prepareStatement(query,
        ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
    } else {
      m_PreparedStatement = m_Connection.prepareStatement(query,
        getSupportedCursorScrollType(), ResultSet.CONCUR_READ_ONLY);
    }

    return (m_PreparedStatement.execute());
  }

  /**
   * Gets the results generated by a previous query. Caller must clean up
   * manually with <code>close(ResultSet)</code>. Returns null if object has
   * been deserialized.
   * 
   * @return the result set.
   * @throws SQLException if an error occurs
   * @see #close(ResultSet)
   */
  public ResultSet getResultSet() throws SQLException {
    if (m_PreparedStatement != null) {
      return m_PreparedStatement.getResultSet();
    } else {
      return null;
    }
  }

  /**
   * Executes a SQL DDL query or an INSERT, DELETE or UPDATE.
   * 
   * @param query the SQL DDL query
   * @return the number of affected rows
   * @throws SQLException if an error occurs
   */
  public int update(String query) throws SQLException {
    if (!isConnected()) {
      throw new IllegalStateException("Not connected, please connect first!");
    }

    Statement statement;
    if (!isCursorScrollable()) {
      statement = m_Connection.createStatement(ResultSet.TYPE_FORWARD_ONLY,
        ResultSet.CONCUR_READ_ONLY);
    } else {
      statement = m_Connection.createStatement(getSupportedCursorScrollType(),
        ResultSet.CONCUR_READ_ONLY);
    }
    int result = statement.executeUpdate(query);
    statement.close();

    return result;
  }

  /**
   * Executes a SQL SELECT query that returns a ResultSet. Note: the ResultSet
   * object must be closed by the caller.
   * 
   * @param query the SQL query
   * @return the generated ResultSet
   * @throws SQLException if an error occurs
   */
  public ResultSet select(String query) throws SQLException {
    if (!isConnected()) {
      throw new IllegalStateException("Not connected, please connect first!");
    }

    Statement statement;
    if (!isCursorScrollable()) {
      statement = m_Connection.createStatement(ResultSet.TYPE_FORWARD_ONLY,
        ResultSet.CONCUR_READ_ONLY);
    } else {
      statement = m_Connection.createStatement(getSupportedCursorScrollType(),
        ResultSet.CONCUR_READ_ONLY);
    }
    ResultSet result = statement.executeQuery(query);

    return result;
  }

  /**
   * closes the ResultSet and the statement that generated the ResultSet to
   * avoid memory leaks in JDBC drivers - in contrast to the JDBC specs, a lot
   * of JDBC drives don't clean up correctly.
   * 
   * @param rs the ResultSet to clean up
   */
  public void close(ResultSet rs) {
    try {
      Statement statement = rs.getStatement();
      rs.close();
      statement.close();
      statement = null;
      rs = null;
    } catch (Exception e) {
      // ignored
    }
  }

  /**
   * closes the m_PreparedStatement to avoid memory leaks.
   */
  public void close() {
    if (m_PreparedStatement != null) {
      try {
        m_PreparedStatement.close();
        m_PreparedStatement = null;
      } catch (Exception e) {
        // ignored
      }
    }
  }

  /**
   * Checks that a given table exists.
   * 
   * @param tableName the name of the table to look for.
   * @return true if the table exists.
   * @throws Exception if an error occurs.
   */
  public boolean tableExists(String tableName) throws Exception {
    if (!isConnected()) {
      throw new IllegalStateException("Not connected, please connect first!");
    }

    if (m_Debug) {
      System.err.println("Checking if table " + tableName + " exists...");
    }
    DatabaseMetaData dbmd = m_Connection.getMetaData();
    ResultSet rs;
    if (m_checkForUpperCaseNames) {
      rs = dbmd.getTables(null, null, tableName.toUpperCase(), null);
    } else if (m_checkForLowerCaseNames) {
      rs = dbmd.getTables(null, null, tableName.toLowerCase(), null);
    } else {
      rs = dbmd.getTables(null, null, tableName, null);
    }
    boolean tableExists = rs.next();
    if (rs.next()) {
      throw new Exception("This table seems to exist more than once!");
    }
    rs.close();
    if (m_Debug) {
      if (tableExists) {
        System.err.println("... " + tableName + " exists");
      } else {
        System.err.println("... " + tableName + " does not exist");
      }
    }
    return tableExists;
  }

  /**
   * processes the string in such a way that it can be stored in the database,
   * i.e., it changes backslashes into slashes and doubles single quotes.
   * 
   * @param s the string to work on
   * @return the processed string
   */
  public static String processKeyString(String s) {
    return s.replaceAll("\\\\", "/").replaceAll("'", "''");
  }

  /**
   * Executes a database query to see whether a result for the supplied key is
   * already in the database.
   * 
   * @param tableName the name of the table to search for the key in
   * @param rp the ResultProducer who will generate the result if required
   * @param key the key for the result
   * @return true if the result with that key is in the database already
   * @throws Exception if an error occurs
   */
  protected boolean isKeyInTable(String tableName, ResultProducer rp,
    Object[] key) throws Exception {

    String query = "SELECT Key_Run" + " FROM " + tableName;
    String[] keyNames = rp.getKeyNames();
    if (keyNames.length != key.length) {
      throw new Exception("Key names and key values of different lengths");
    }
    boolean first = true;
    for (int i = 0; i < key.length; i++) {
      if (key[i] != null) {
        if (first) {
          query += " WHERE ";
          first = false;
        } else {
          query += " AND ";
        }
        query += "Key_" + keyNames[i] + '=';
        if (key[i] instanceof String) {
          query += "'" + processKeyString(key[i].toString()) + "'";
        } else {
          query += key[i].toString();
        }
      }
    }
    boolean retval = false;
    ResultSet rs = select(query);
    if (rs.next()) {
      retval = true;
      if (rs.next()) {
        throw new Exception("More than one result entry " + "for result key: "
          + query);
      }
    }
    close(rs);
    return retval;
  }

  /**
   * Executes a database query to extract a result for the supplied key from the
   * database.
   * 
   * @param tableName the name of the table where the result is stored
   * @param rp the ResultProducer who will generate the result if required
   * @param key the key for the result
   * @return true if the result with that key is in the database already
   * @throws Exception if an error occurs
   */
  public Object[] getResultFromTable(String tableName, ResultProducer rp,
    Object[] key) throws Exception {

    String query = "SELECT ";
    String[] resultNames = rp.getResultNames();
    for (int i = 0; i < resultNames.length; i++) {
      if (i != 0) {
        query += ", ";
      }
      query += resultNames[i];
    }
    query += " FROM " + tableName;
    String[] keyNames = rp.getKeyNames();
    if (keyNames.length != key.length) {
      throw new Exception("Key names and key values of different lengths");
    }
    boolean first = true;
    for (int i = 0; i < key.length; i++) {
      if (key[i] != null) {
        if (first) {
          query += " WHERE ";
          first = false;
        } else {
          query += " AND ";
        }
        query += "Key_" + keyNames[i] + '=';
        if (key[i] instanceof String) {
          query += "'" + processKeyString(key[i].toString()) + "'";
        } else {
          query += key[i].toString();
        }
      }
    }
    ResultSet rs = select(query);
    ResultSetMetaData md = rs.getMetaData();
    int numAttributes = md.getColumnCount();
    if (!rs.next()) {
      throw new Exception("No result for query: " + query);
    }
    // Extract the columns for the result
    Object[] result = new Object[numAttributes];
    for (int i = 1; i <= numAttributes; i++) {
      switch (translateDBColumnType(md.getColumnTypeName(i))) {
      case STRING:
        result[i - 1] = rs.getString(i);
        if (rs.wasNull()) {
          result[i - 1] = null;
        }
        break;
      case FLOAT:
      case DOUBLE:
        result[i - 1] = new Double(rs.getDouble(i));
        if (rs.wasNull()) {
          result[i - 1] = null;
        }
        break;
      default:
        throw new Exception("Unhandled SQL result type (field " + (i + 1)
          + "): " + DatabaseUtils.typeName(md.getColumnType(i)));
      }
    }
    if (rs.next()) {
      throw new Exception("More than one result entry " + "for result key: "
        + query);
    }
    close(rs);
    return result;
  }

  /**
   * Executes a database query to insert a result for the supplied key into the
   * database.
   * 
   * @param tableName the name of the table where the result is stored
   * @param rp the ResultProducer who will generate the result if required
   * @param key the key for the result
   * @param result the result to store
   * @throws Exception if an error occurs
   */
  public void putResultInTable(String tableName, ResultProducer rp,
    Object[] key, Object[] result) throws Exception {

    String query = "INSERT INTO " + tableName + " VALUES ( ";
    // Add the results to the table
    for (int i = 0; i < key.length; i++) {
      if (i != 0) {
        query += ',';
      }
      if (key[i] != null) {
        if (key[i] instanceof String) {
          query += "'" + processKeyString(key[i].toString()) + "'";
        } else if (key[i] instanceof Double) {
          query += safeDoubleToString((Double) key[i]);
        } else {
          query += key[i].toString();
        }
      } else {
        query += "NULL";
      }
    }
    for (Object element : result) {
      query += ',';
      if (element != null) {
        if (element instanceof String) {
          query += "'" + element.toString() + "'";
        } else if (element instanceof Double) {
          query += safeDoubleToString((Double) element);
        } else {
          query += element.toString();
          // !!
          // System.err.println("res: "+ result[i].toString());
        }
      } else {
        query += "NULL";
      }
    }
    query += ')';

    if (m_Debug) {
      System.err.println("Submitting result: " + query);
    }
    update(query);
    close();
  }

  /**
   * Inserts a + if the double is in scientific notation. MySQL doesn't
   * understand the number otherwise.
   * 
   * @param number the number to convert
   * @return the number as string
   */
  private String safeDoubleToString(Double number) {
    // NaN is treated as NULL
    if (number.isNaN()) {
      return "NULL";
    }

    String orig = number.toString();

    int pos = orig.indexOf('E');
    if ((pos == -1) || (orig.charAt(pos + 1) == '-')) {
      return orig;
    } else {
      StringBuffer buff = new StringBuffer(orig);
      buff.insert(pos + 1, '+');
      return new String(buff);
    }
  }

  /**
   * Returns true if the experiment index exists.
   * 
   * @return true if the index exists
   * @throws Exception if an error occurs
   */
  public boolean experimentIndexExists() throws Exception {
    return tableExists(EXP_INDEX_TABLE);
  }

  /**
   * Attempts to create the experiment index table.
   * 
   * @throws Exception if an error occurs.
   */
  public void createExperimentIndex() throws Exception {
    if (m_Debug) {
      System.err.println("Creating experiment index table...");
    }
    String query;

    // Workaround for MySQL (doesn't support LONGVARBINARY)
    // Also for InstantDB which attempts to interpret numbers when storing
    // in LONGVARBINARY
    /*
     * if (m_Connection.getMetaData().getDriverName().
     * equals("Mark Matthews' MySQL Driver") ||
     * (m_Connection.getMetaData().getDriverName().
     * indexOf("InstantDB JDBC Driver") != -1)) { query = "CREATE TABLE " +
     * EXP_INDEX_TABLE + " ( " + EXP_TYPE_COL + " TEXT," + "  " + EXP_SETUP_COL
     * + " TEXT," + "  " + EXP_RESULT_COL + " INT )"; } else {
     */

    query = "CREATE TABLE " + EXP_INDEX_TABLE + " ( " + EXP_TYPE_COL + " "
      + m_stringType + "," + "  " + EXP_SETUP_COL + " " + m_stringType + ","
      + "  " + EXP_RESULT_COL + " " + m_intType + " )";
    // }
    // Other possible fields:
    // creator user name (from System properties)
    // creation date
    update(query);
    close();
  }

  /**
   * Attempts to insert a results entry for the table into the experiment index.
   * 
   * @param rp the ResultProducer generating the results
   * @return the name of the created results table
   * @throws Exception if an error occurs.
   */
  public String createExperimentIndexEntry(ResultProducer rp) throws Exception {

    if (m_Debug) {
      System.err.println("Creating experiment index entry...");
    }

    // Execute compound transaction
    int numRows = 0;

    // Workaround for MySQL (doesn't support transactions)
    /*
     * if (m_Connection.getMetaData().getDriverName().
     * equals("Mark Matthews' MySQL Driver")) {
     * m_Statement.execute("LOCK TABLES " + EXP_INDEX_TABLE + " WRITE");
     * System.err.println("LOCKING TABLE"); } else {
     */

    // }

    // Get the number of rows
    String query = "SELECT COUNT(*) FROM " + EXP_INDEX_TABLE;
    ResultSet rs = select(query);
    if (m_Debug) {
      System.err.println("...getting number of rows");
    }
    if (rs.next()) {
      numRows = rs.getInt(1);
    }
    close(rs);

    // Add an entry in the index table
    String expType = rp.getClass().getName();
    String expParams = rp.getCompatibilityState();
    query = "INSERT INTO " + EXP_INDEX_TABLE + " VALUES ('" + expType + "', '"
      + expParams + "', " + numRows + " )";
    if (update(query) > 0) {
      if (m_Debug) {
        System.err.println("...create returned resultset");
      }
    }
    close();

    // Finished compound transaction
    // Workaround for MySQL (doesn't support transactions)
    /*
     * if (m_Connection.getMetaData().getDriverName().
     * equals("Mark Matthews' MySQL Driver")) {
     * m_Statement.execute("UNLOCK TABLES");
     * System.err.println("UNLOCKING TABLE"); } else {
     */
    if (!m_setAutoCommit) {
      m_Connection.commit();
      m_Connection.setAutoCommit(true);
    }
    // }

    String tableName = getResultsTableName(rp);
    if (tableName == null) {
      throw new Exception("Problem adding experiment index entry");
    }

    // Drop any existing table by that name (shouldn't occur unless
    // the experiment index is destroyed, in which case the experimental
    // conditions of the existing table are unknown)
    try {
      query = "DROP TABLE " + tableName;
      if (m_Debug) {
        System.err.println(query);
      }
      update(query);
    } catch (SQLException ex) {
      System.err.println(ex.getMessage());
    }
    return tableName;
  }

  /**
   * Gets the name of the experiment table that stores results from a particular
   * ResultProducer.
   * 
   * @param rp the ResultProducer
   * @return the name of the table where the results for this ResultProducer are
   *         stored, or null if there is no table for this ResultProducer.
   * @throws Exception if an error occurs
   */
  public String getResultsTableName(ResultProducer rp) throws Exception {
    // Get the experiment table name, or create a new table if necessary.
    if (m_Debug) {
      System.err.println("Getting results table name...");
    }
    String expType = rp.getClass().getName();
    String expParams = rp.getCompatibilityState();
    String query = "SELECT " + EXP_RESULT_COL + " FROM " + EXP_INDEX_TABLE
      + " WHERE " + EXP_TYPE_COL + "='" + expType + "' AND " + EXP_SETUP_COL
      + "='" + expParams + "'";
    String tableName = null;
    ResultSet rs = select(query);
    if (rs.next()) {
      tableName = rs.getString(1);
      if (rs.next()) {
        throw new Exception("More than one index entry "
          + "for experiment config: " + query);
      }
    }
    close(rs);
    if (m_Debug) {
      System.err.println("...results table = "
        + ((tableName == null) ? "<null>" : EXP_RESULT_PREFIX + tableName));
    }
    return (tableName == null) ? tableName : EXP_RESULT_PREFIX + tableName;
  }

  /**
   * Creates a results table for the supplied result producer.
   * 
   * @param rp the ResultProducer generating the results
   * @param tableName the name of the resultsTable
   * @return the name of the created results table
   * @throws Exception if an error occurs.
   */
  public String createResultsTable(ResultProducer rp, String tableName)
    throws Exception {

    if (m_Debug) {
      System.err.println("Creating results table " + tableName + "...");
    }
    String query = "CREATE TABLE " + tableName + " ( ";
    // Loop over the key fields
    String[] names = rp.getKeyNames();
    Object[] types = rp.getKeyTypes();
    if (names.length != types.length) {
      throw new Exception("key names types differ in length");
    }
    for (int i = 0; i < names.length; i++) {
      query += "Key_" + names[i] + " ";
      if (types[i] instanceof Double) {
        query += m_doubleType;
      } else if (types[i] instanceof String) {

        // Workaround for MySQL (doesn't support LONGVARCHAR)
        // Also for InstantDB which attempts to interpret numbers when storing
        // in LONGVARBINARY
        /*
         * if (m_Connection.getMetaData().getDriverName().
         * equals("Mark Matthews' MySQL Driver") ||
         * (m_Connection.getMetaData().getDriverName().
         * indexOf("InstantDB JDBC Driver")) != -1) { query += "TEXT "; } else {
         */
        // query += "LONGVARCHAR ";
        query += m_stringType + " ";
        // }
      } else {
        throw new Exception("Unknown/unsupported field type in key");
      }
      query += ", ";
    }
    // Loop over the result fields
    names = rp.getResultNames();
    types = rp.getResultTypes();
    if (names.length != types.length) {
      throw new Exception("result names and types differ in length");
    }
    for (int i = 0; i < names.length; i++) {
      query += names[i] + " ";
      if (types[i] instanceof Double) {
        query += m_doubleType;
      } else if (types[i] instanceof String) {

        // Workaround for MySQL (doesn't support LONGVARCHAR)
        // Also for InstantDB which attempts to interpret numbers when storing
        // in LONGVARBINARY
        /*
         * if (m_Connection.getMetaData().getDriverName().
         * equals("Mark Matthews' MySQL Driver") ||
         * (m_Connection.getMetaData().getDriverName().
         * equals("InstantDB JDBC Driver"))) { query += "TEXT "; } else {
         */
        // query += "LONGVARCHAR ";
        query += m_stringType + " ";
        // }
      } else {
        throw new Exception("Unknown/unsupported field type in key");
      }
      if (i < names.length - 1) {
        query += ", ";
      }
    }
    query += " )";

    update(query);
    if (m_Debug) {
      System.err.println("table created");
    }
    close();

    if (m_createIndex) {
      query = "CREATE UNIQUE INDEX Key_IDX ON " + tableName + " (";

      String[] keyNames = rp.getKeyNames();

      boolean first = true;
      for (String keyName : keyNames) {
        if (keyName != null) {
          if (first) {
            first = false;
            query += "Key_" + keyName;
          } else {
            query += ",Key_" + keyName;
          }
        }
      }
      query += ")";

      update(query);
    }
    return tableName;
  }

  /**
   * Sets the keywords (comma-separated list) to use.
   * 
   * @param value the list of keywords
   */
  public void setKeywords(String value) {
    String[] keywords;
    int i;

    m_Keywords.clear();

    keywords = value.replaceAll(" ", "").split(",");
    for (i = 0; i < keywords.length; i++) {
      m_Keywords.add(keywords[i].toUpperCase());
    }
  }

  /**
   * Returns the currently stored keywords (as comma-separated list).
   * 
   * @return the list of keywords
   */
  public String getKeywords() {
    String result;
    Vector<String> list;
    int i;

    list = new Vector<String>(m_Keywords);
    Collections.sort(list);

    result = "";
    for (i = 0; i < list.size(); i++) {
      if (i > 0) {
        result += ",";
      }
      result += list.get(i);
    }

    return result;
  }

  /**
   * Sets the mask character to append to table or attribute names that are a
   * reserved keyword.
   * 
   * @param value the new character
   */
  public void setKeywordsMaskChar(String value) {
    m_KeywordsMaskChar = value;
  }

  /**
   * Returns the currently set mask character.
   * 
   * @return the character
   */
  public String getKeywordsMaskChar() {
    return m_KeywordsMaskChar;
  }

  /**
   * Checks whether the given string is a reserved keyword.
   * 
   * @param s the string to check
   * @return true if the string is a keyword
   * @see #m_Keywords
   */
  public boolean isKeyword(String s) {
    return m_Keywords.contains(s.toUpperCase());
  }

  /**
   * If the given string is a keyword, then the mask character will be appended
   * and returned. Otherwise, the same string will be returned unchanged.
   * 
   * @param s the string to check
   * @return the potentially masked string
   * @see #m_KeywordsMaskChar
   * @see #isKeyword(String)
   */
  public String maskKeyword(String s) {
    if (isKeyword(s)) {
      return s + m_KeywordsMaskChar;
    } else {
      return s;
    }
  }

  /**
   * Returns the revision string.
   * 
   * @return the revision
   */
  @Override
  public String getRevision() {
    return RevisionUtils.extract("$Revision: 11887 $");
  }
}
