Kristian:

thank you for being so observant. Actually, it was a programmatic typo on my part, as I just tried to type the pseudo-code into the email.
My production code does follow the described pattern:

    final public Object getValue(ResultSet resultSet) throws SQLException {
        final Object object = resultSet.getObject(m_columnIdx);
        if (resultSet.wasNull()) {
            return null;
        }
        return object;
    }

/******************************************/

                    final Object object = resultSet.getObject(i);
                    String string;
                    if (object == null || resultSet.wasNull()) {
                        string = m_nullValueIndicator;
                    } else {
                        switch (columnTypes[i]) {

/******************************************/

        while (resultSet.next()) {
            tableBuilder.append("<TR>");
            for (int i = 1; i <= columnCount; i++) {
                final String string = resultSet.getString(i);
                final String value = (string == null || resultSet.wasNull() ? "&nbsp;" : string.trim());
                tableBuilder.append("<TD>").append(value).append("</TD>");
            }
            tableBuilder.append("</TR>\n");
        }


Much appreciated,
Pavel.





Kristian Waagan <Kristian.Waagan@Sun.COM>
Sent by: Kristian.Waagan@Sun.COM

06/10/2010 04:59 AM
Please respond to
"Derby Discussion" <derby-user@db.apache.org>

To
derby-user@db.apache.org
cc
Subject
Re: Resetting ResultSet with first() or beforeFirst()





On 09.06.10 19:32, Pavel Bortnovskiy wrote:
>
> Hi:
>
> I am trying to reset a given ResultSet back to the first record, so that
> I could iterate through its records one more time, after it's already
> been done once. So, my code does something like this (it's pseudo-code,
> and in the real application these two passes are done in different parts
> of the application):
>
> // get ResultSet
> final ResultSet resultSet = ((PreparedStatement)
> m_statement).executeQuery();
> final int columnCount = resultSet.getMetaData().getColumnCount();
> // First Pass through the data
> while (resultSet.next()) {
> for (int i = 1; i <= columnCount; i++) {
> if (resultSet.wasNull()) {

Hi,

I don't know of this issue is present in your actual code, but note that
ResultSet.wasNull must be called *after* a getter method has been called.
From the JavaDocs:

"Reports whether the last column read had a value of SQL NULL. Note that
you must first call one of the getter methods on a column to try to read
its value and then call the method wasNull to see if the value read was
SQL NULL."

> doSomethingWithNULL();
> } else {
> doSomethingWithObject(resultSet.getObject(i));

Assuming wasNull was called after the getter method, the second
getObject above may raise an exception in Derby. The restriction that
you can call a getter only once for a given column is limited to some
data types (i.e. BLOB and CLOB) and some getters (getXXXStream,
getObject for the data types mentioned).

Just thought I'd mention it :)


Regards,
--
Kristian

> }
> }
> }
> // Reset ResultSet - but it generates SQLException: The 'beforeFirst()'
> method is only allowed on scroll cursors
> resultSet.beforeFirst();
> // Second Pass through the data
> while (resultSet.next()) {
> for (int i = 1; i <= columnCount; i++) {
> if (resultSet.wasNull()) {
> doSomethingElseWithNULL();
> } else {
> doSomethingElseWithObject(resultSet.getObject(i));
> }
> }
> }
>
>
> However, resultSet.beforeFirst() generates an exception:
>
> java.sql.SQLException: The 'beforeFirst()' method is only allowed on
> scroll cursors.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown Source)
> at org.apache.derby.impl.jdbc.EmbedResultSet.checkScrollCursor(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedResultSet.beforeFirst(Unknown Source)
> Caused by: java.sql.SQLException: The 'beforeFirst()' method is only
> allowed on scroll cursors.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown
> Source)
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown
> Source)
> ... 8 more
>
> Could someone please help me out to understand what may be done
> incorrectly and what would be the right approach to enable two-pass
> logic through the RecordSet?
>
> Thanks,
>
> Pavel.
>
>
>
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