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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