On Fri, Dec 10, 2004 at 11:32:37AM -0000, Martin J. Evans wrote:
> The DBI documentation for LongReadLen includes:
>
> "A value of 0 means not to automatically fetch any long data. ("fetch" should
> return "undef" for long fields when "LongReadLen" is 0.)"
>
> What is the significance of the "automatically"?
Probably a vague nod towards the possibility that some drivers may
supply extra methods for reading blobs (in chunks etc).
But I doubt any drivers do exactly what's specified here.
Most probably just truncate to a 0 length string rather than
return undef. I may loosen the spec to say that a driver
"may" return undef for LONG type fields if LongReadLen is 0.
> Should the following code on a long column (MS SQL Server text column) return
> undef for col2 or the error I've included?
>
> $sth->{LongReadLen} = 0;
> print "LongTruncOk is '", $sth->{LongTruncOk}, "'\n";
> print "LongReadLen is ", $sth->{LongReadLen}, "\n";
> $sth = $dbh->prepare(q/select * from table/);
> $sth->execute;
> my ($col1, $col2);
> $sth->bind_columns(\($col1, $col2));
> while ($sth->fetch) {
> print "$col1, $col2\n";
> }
>
> LongTruncOk is ''
> LongReadLen is 0
> DBD::ODBC::st fetch failed: [unixODBC][][Microsoft][ODBC SQL Server
> Driver]String data, right truncation (SQL-01004)(DBD: st_fetch/SQLFetch (long
> truncated DBI attribute LongTruncOk not set and/or LongReadLen too small)
> err=-1) at ./tut2_9.pl line 24.
LongTruncOk is false so therefore it's an error for a long to be
truncated by LongReadLen. So the error is correct.
Tim.
