Re: Resetting ResultSet with first() or beforeFirst()
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.waa...@sun.com
Sent by: kristian.waa...@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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arising as a result
Resetting ResultSet with first() or beforeFirst()
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?
Thanks,
Pavel.
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.
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
Re: Resetting ResultSet with first() or beforeFirst()
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.
