Thank you, Knut.
Is there a large performance penalty for specifying
ResultSet.TYPE_SCROLL_INSENSITIVE, ||ResultSet.CONCUR_READ_ONLY?
For the sake of efficiency, should my code set those only when it is
necessary to reset the ResultSet?
Pavel.
Knut Anders Hatlen <knut.hat...@sun.com>
Sent by: knut.hat...@sun.com
06/09/2010 06:21 PM
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 06/ 9/10 07:32 PM, 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()) {
> doSomethingWithNULL();
> } else {
> doSomethingWithObject(resultSet.getObject(i));
> }
> }
> }
> // 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?
You need to specify that the result should be scrollable when you
prepare the statement. Something like this:
PreparedStatement ps = conn.prepareStatement(
sql, |ResultSet.TYPE_SCROLL_INSENSITIVE,
||ResultSet.CONCUR_READ_ONLY);|
--
Knut Anders
Jefferies archives and monitors outgoing and incoming e-mail. The contents of
this email, including any attachments, are confidential to the ordinary user of
the email address to which it was addressed. If you are not the addressee of
this email you may not copy, forward, disclose or otherwise use it or any part
of it in any form whatsoever. This email may be produced at the request of
regulators or in connection with civil litigation. Jefferies accepts no
liability for any errors or omissions arising as a result of transmission. Use
by other than intended recipients is prohibited. In the United Kingdom,
Jefferies operates as Jefferies International Limited; registered in England:
no. 1978621; registered office: Vintners Place, 68 Upper Thames Street, London
EC4V 3BJ. Jefferies International Limited is authorised and regulated by the
Financial Services Authority.
