jdbcresultsetmetadata.java

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/* Copyright (c) 2001-2005, The HSQL Development Group
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
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 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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package org.hsqldb.jdbc;

import java.sql.ResultSetMetaData;
import java.sql.SQLException;

import org.hsqldb.Result;
import org.hsqldb.ResultConstants;
import org.hsqldb.Trace;
import org.hsqldb.Types;
import org.hsqldb.persist.HsqlProperties;

// fredt@users 20040412 - removed DITypeInfo dependencies
// boucherb@users - 200404xx - removed unused imports;refinement for better
//                             usability of getColumnDisplaySize;
//                             javadoc updates

/**
 * <!-- start generic documentation -->
 * An object that can be used to get information about the types
 * and properties of the columns in a <code>ResultSet</code> object.
 * The following code fragment creates the <code>ResultSet</code>
 * object rs, creates the <code>ResultSetMetaData</code> object rsmd,
 * and uses rsmd to find out how many columns rs has and whether the
 * first column in rs can be used in a <code>WHERE</code> clause.
 * <PRE>
 *
 * ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM TABLE2");
 * ResultSetMetaData rsmd = rs.getMetaData();
 * int numberOfColumns = rsmd.getColumnCount();
 * boolean b = rsmd.isSearchable(1);
 *
 * </PRE>
 * <!-- end generic documentation -->
 *
 * <!-- start Release-specific documentation -->
 * <div class="ReleaseSpecificDocumentation">
 * <h3>HSQLDB-Specific Information:</h3> <p>
 *
 * HSQLDB supports a subset of the <code>ResultSetMetaData</code> interface.<p>
 *
 * The JDBC specification for <code>ResultSetMetaData</code> is in part very
 * vague. This causes potential incompatibility between interpretations of the
 * specification as realized in different JDBC driver implementations. As such,
 * deciding to what degree reporting ResultSetMetaData is accurate has been
 * considered very carefully. Hopefully, the design decisions made in light of
 * these considerations have yeilded precisely the subset of full
 * ResultSetMetaData support that is most commonly needed and that is most
 * important, while also providing, under the most common use-cases, the
 * fastest access with the least overhead and the best comprimise between
 * speed, accuracy, jar-foootprint and retention of JDBC resources. <p>
 *
 * (fredt@users) <br>
 * (boucherb@users)<p>
 * </div>
 * <!-- end release-specific documentation -->
 *
 * @author boucherb@users
 * @version 1.7.2
 * @see jdbcStatement#executeQuery
 * @see jdbcStatement#getResultSet
 * @see java.sql.ResultSetMetaData
 */
public class jdbcResultSetMetaData implements ResultSetMetaData {

    /**
     * An array of objects, each of which represents the reported attributes
     * for  a single column of this object's parent ResultSet.
     */
    private jdbcColumnMetaData[] columnMetaData;

    /** The number of columns in this object's parent ResultSet. */
    private int columnCount;

    /**
     * Whether to use the underlying column name or label when reporting
     * getColumnName().
     */
    private boolean useColumnName;

    /**
     * If true, then timings for init() are printed
     * to the console.
     */
    private static final boolean TRACE = false;

    /**
     * Constructs a new jdbcResultSetMetaData object from the specified
     * jdbcResultSet and HsqlProprties objects.
     *
     * @param rs the jdbcResultSet object from which to construct a new
     *        jdbcResultSetMetaData object
     * @param props the HsqlProperties object from which to construct a
     *        new jdbcResultSetMetaData object
     * @throws SQLException if a database access error occurs
     */
    jdbcResultSetMetaData(jdbcResultSet rs,
                          HsqlProperties props) throws SQLException {
        init(rs, props);
    }

    /**
     * Constructs a new jdbcResultSetMetaData object from the specified
     * Result and HsqlProprties objects.
     *
     * @param r the Result object from which to construct a new
     *        jdbcResultSetMetaData object
     * @param props the HsqlProperties object from which to construct a
     *        new jdbcResultSetMetaData object
     * @throws SQLException if a database access error occurs
     */
    jdbcResultSetMetaData(Result r,
                          HsqlProperties props) throws SQLException {
        init(r, props);
    }

    /**
     * Initializes this jdbcResultSetMetaData object from the specified
     * jdbcResultSet and HsqlProperties objects.
     *
     * @param rs the jdbcResultSet object from which to initialize this
     *        jdbcResultSetMetaData object
     * @param props the HsqlProperties object from which to initialize this
     *        jdbcResultSetMetaData object
     * @throws SQLException if a database access error occurs
     */
    void init(jdbcResultSet rs, HsqlProperties props) throws SQLException {

        if (rs == null) {
            throw Util.sqlException(Trace.GENERAL_ERROR,
                                    Trace.JDBC_NO_RESULT_SET_METADATA, null);
        }

        init(rs.rResult, props);
    }

    /**
     * Initializes this jdbcResultSetMetaData object from the specified
     * Result and HsqlProperties objects.
     *
     * @param r the Result object from which to initialize this
     *        jdbcResultSetMetaData object
     * @param props the HsqlProperties object from which to initialize this
     *        jdbcResultSetMetaData object
     * @throws SQLException if a database access error occurs
     */
    void init(Result r, HsqlProperties props) throws SQLException {

        jdbcColumnMetaData    cmd;
        int                   type;
        Result.ResultMetaData rmd;

        if (r == null) {
            throw Util.sqlException(Trace.GENERAL_ERROR,
                                    Trace.JDBC_NO_RESULT_SET, null);
        }

        if (!r.isData()) {

            // implied: columnCount = 0;
            return;
        }

        columnCount = r.getColumnCount();

        // fredt -  props is null for internal connections, so always use the default behaviour in this case
        useColumnName = props == null ? true
                                      : props.isPropertyTrue(
                                          "get_column_name");
        columnMetaData = new jdbcColumnMetaData[columnCount];
        rmd            = r.metaData;

        for (int i = 0; i < columnCount; i++) {
            cmd               = new jdbcColumnMetaData();
            columnMetaData[i] = cmd;

            // Typically, these null checks are not needed, but as
            // above, it is not _guaranteed_ that these values
            // will be non-null.   So, it is better to do the work
            // here than have to perform checks and conversions later.
            cmd.catalogName = rmd.catalogNames[i] == null ? ""
                                                          : rmd
                                                          .catalogNames[i];
            cmd.schemaName     = rmd.schemaNames[i] == null ? ""
                                                            : rmd
                                                            .schemaNames[i];
            cmd.tableName      = rmd.tableNames[i] == null ? ""
                                                           : rmd
                                                           .tableNames[i];
            cmd.columnName     = rmd.colNames[i] == null ? ""
                                                         : rmd.colNames[i];
            cmd.columnLabel    = rmd.colLabels[i] == null ? ""
                                                          : rmd.colLabels[i];
            cmd.columnType     = rmd.colTypes[i];
            cmd.columnTypeName = Types.getTypeString(cmd.columnType);
            cmd.isWritable     = rmd.isWritable[i];
            cmd.isReadOnly     = !cmd.isWritable;

            // default: cmd.isDefinitelyWritable = false;
            cmd.isAutoIncrement = rmd.isIdentity[i];
            cmd.isNullable      = rmd.colNullable[i];
            type                = cmd.columnType;
            cmd.columnClassName = rmd.classNames[i];

            if (cmd.columnClassName == null
                    || cmd.columnClassName.length() == 0) {
                cmd.columnClassName = Types.getColStClsName(type);
            }

            // Some tools, such as PowerBuilder, require that (for char and
            // varchar types, at any rate) getMaxDisplaySize returns a value
            // _at least_ as large as the length of the longest value in this
            // column of the result set, or else an internal error will occur
            // at retrieve time the instant a longer value is fetched.
            //
            // org.hsqldb.Types has been patched to retrieve, by default, either
            // a large-but-reasonable value or a value defined through system
            // properties that is expected to be unlikely to cause problems in
            // the majority of cases.
            if (Types.acceptsPrecisionCreateParam(type)) {
                if (rmd.colSizes[i] == 0) {
                    cmd.columnDisplaySize = Types.getMaxDisplaySize(type);
                } else {
                    cmd.columnDisplaySize = rmd.colSizes[i];

                    if (Types.acceptsScaleCreateParam(type)) {
                        if (rmd.colScales[i] != 0) {
                            cmd.columnDisplaySize += (1 + rmd.colScales[i]);
                        }
                    }
                }
            } else {
                cmd.columnDisplaySize = Types.getMaxDisplaySize(type);
            }

            if (Types.isNumberType(type)
                    && Types.acceptsPrecisionCreateParam(type)) {
                cmd.precision = rmd.colSizes[i];

                if (cmd.precision == 0) {
                    cmd.precision = Types.getPrecision(type);
                }
            } else {
                cmd.precision = Types.getPrecision(type);
            }

            // Without a non-zero scale value, some (legacy only?) tools will
            // simply truncate digits to the right of the decimal point when
            // retrieving values from the result set. The measure below can
            // help, but currently only as long as one is connected to an
            // embedded instance at design time, not via a network connection.
            if (Types.acceptsScaleCreateParam(type)) {
                cmd.scale = rmd.colScales[i];
            }

            Boolean iua = Types.isUnsignedAttribute(type);

            cmd.isSigned = iua != null &&!iua.booleanValue();

            Boolean ics = Types.isCaseSensitive(type);

            cmd.isCaseSensitive = ics != null && ics.booleanValue();
            cmd.isSearchable    = Types.isSearchable(type);
        }
    }

    /**
     * <!-- start generic documentation -->
     * Returns the number of columns in this <code>ResultSet</code>
     * object. <p>
     * <!-- end generic documentation -->
     * @return the number of columns
     * @exception SQLException if a database access error occurs
     */
    public int getColumnCount() throws SQLException {
        return columnCount;
    }

    /**
     * <!-- start generic documentation -->
     * Indicates whether the designated column is automatically numbered,
     * thus read-only. <p>
     * <!-- end generic documentation -->
     *
     * <!-- start Release-specific documentation -->
     * <div class="ReleaseSpecificDocumentation">
     * <h3>HSQLDB-Specific Information:</h3> <p>
     *
     * HSQLDB 1.7.1 did not report this value accurately,
     * either always throwing or always returning false, depending
     * upon client property values.<p>
     *
     * Starting with HSQLDB 1.7.2, this feature is better supported. <p>
     *
     * <hr>
     *
     * However, it must be stated here that, contrary to the generic
     * documentation above, HSQLDB automatically numbered columns
     * (IDENTITY columns, in HSQLDB parlance) are not read-only. <p>
     *
     * In fact, the generic documentation above seems to contradict the general
     * definition of what, at minimum, an auto-increment column is: <p>
     *
     * Simply, an auto-increment column is one that guarantees it has a
     * unique value after a successful insert or update operation, even if
     * no value is supplied or NULL is explicitly specified by the application
     * or a default value expression. <p>
     *
     * Further, without SQL Feature T176, Sequence generator support, the
     * attributes of the internal source consulted for unique values are not
     * defined. That is, unlike for a standard SQL SEQUENCE object or a system
     * with full SQL 9x or 200n support for SQL Feature T174, Identity columns,
     * an application must not assume and cannot determine in a standard way
     * that auto-increment values start at any particular point, increment by
     * any particular value or have any of the other attributes generally
     * associated with SQL SEQUENCE generators. Further still, without full
     * support for both feature T174 and T176, if a unique value is supplied
     * by an application or provided by a declared or implicit default value
     * expression, then whether that value is used or substituted with one
     * from the automatic unique value  source is implementation-defined
     * and cannot be known in a standard way. Finally, without full support
     * for features T174 and T176, it is also implementation-defined and
     * cannot be know in a standard way whether an exception is thrown or
     * a unique value is automatically substituted when an application or
     * default value expression supplies a non-NULL,
     * non-unique value. <p>
     *
     * Up to and including HSQLDB 1.7.2, values supplied by an application or
     * default value expression are used if they are indeed non-NULL unique
     * values, while an exception is thrown if either possible value source
     * for the site attempts to supply a non-NULL, non-unique value.  This is
     * very likely to remain the behaviour of HSQLDB for its foreseable
     * lifetime and at the very least for the duration of the 1.7.x release
     * series.<p>
     *
     * <hr>
     *
     * Regardless of the new and better support for reporting
     * isAutoIncrement(), it is still possible under certain conditions that
     * accurate reporting may be impossible. For example, if this object's
     * parent Connection is closed before the first call to this method or to
     * any other method of this class that initializes the connection-dependent
     * ResultSetMetaData values, then it is impossible to report accurately for
     * result set columns that directly represent table column values.<p>
     *
     * Under such special circumstances, the driver rethrows the exception that
     * occured during the initialization, or a SQLException wrapping it. <p>
     *
     * Those wishing to determine the auto-increment status of a table column
     * in isolation from ResultSetMetaData can do so by inspecting the
     * corresponding value of the SYSTEM_COLUMNS.IS_IDENTITY BOOLEAN column which
     * is also currently included (in a fashion proprietary to HSQLDB) as the
     * last column of the jdbcDatabaseMetaData.getColumns() result.