On 15/08/12 16:14, Martin J. Evans wrote:
I've just been given an rt https://rt.cpan.org/Ticket/Display.html?id=78838 and am at a loss to explain exactly what is happening. I wonder if anyone can help?Some background: DBI says for bind_param: "The bind_param method takes a copy of $bind_value and associates it (binds it) with a placeholder" As far as I am aware DBD::ODBC does not copy the scalar given to it - so perhaps DBI does this. The problem I'm seeing in the provided example is the pointer passed to ODBC's SQLBindParameter at the time bind_param is called no longer points to a valid string when execute is called. However, changing the call to bind_param to pass $obj as "$obj" appears to fix the problem. Can anyone say if DBD::ODBC should work with either example and explain what might be happening here: use DBI; my $dbh = DBI->connect("dbi:ODBC:DSN=xxx;UID=xx;PWD=yy;MARS_Connection=No;"); my $obj = new Object(); my $sql = q(SELECT ? AS result); my $sth = $dbh->prepare($sql); # interesting - is the following use of $obj really as a string? # in the call to bind_param here, DBD::ODBC binds the pv ptr of the scalar # it is given in a SQLBindParameter call but by the time execute is called # the string at that address is no longer valid. I kind of expect that as # what to_s returns is only required in the bind_param statement and yet # DBI says "bind_param takes a copy". # However if the following is changed to "$obj" it works $sth->bind_param(1, $obj); $sth->execute(); while (my $row = $sth->fetchrow_hashref()) { print $row->{'result'}, "\n"; } package Object; use overload '""' => 'to_s'; sub new() { bless { }, shift }; sub to_s() { my $self = shift; ref($self); } Output when using $obj: value passed to DBD::ODBC's bind_param = "Object" pointer at execute time seems to point to rubbish output of script: 8�k�8 When "$obj" passed to bind_param value passed to DBD::ODBC's bind_param = "Object" pointer at execute time points to "Object" output of script: Object As a quick test I did the following and it seems to work so I guess there is something about the above Perl I don't get.
$obj is not a string. It is an object of a class which has a stringify operator. "$obj" is a string, because "..." stringifies. It is not at all clear how the DBI should take a copy of an object. I think this is a case of user error. -- Charles Jardine - Computing Service, University of Cambridge c...@cam.ac.uk Tel: +44 1223 334506, Fax: +44 1223 334679
