comment on

Hello most gracious monks,

I was happily writing a Catalyst app with DBIx::Class when I tripped over some database problem. I haven't been able to pin it down, but I'm pretty sure it has to do with DBD::Sybase used with our MSSQL server.

My original problem is I tried to call ->first on a DBIx::Class::ResultSet twice. That produced the error "DBIx::Class::ResultSet::first(): Unknown error: execute() returned false, but error flags were not set...", which you can find in DBIx::Class::Storage::DBI in sub _dbh_execute.

  # Can this fail without throwing an exception anyways???
  my $rv = $sth->execute();
  $self->throw_exception(
    $sth->errstr || $sth->err || 'Unknown error: execute() returned fa
+lse, but error flags were not set...'
  ) if !$rv;
[download]

I have a minimal test using only DBI that demonstrates the problem.

use 5.014;
use strict;
use warnings;

use DBI;
use Test::More;

my @connect_info = (
    "dbi:Sybase:server=xxx;database=xxx",
    'xxx',
    ':)',
    { RaiseError => 1 },
);

# @connect_info = ("dbi:SQLite2:dbname=dbfile","","");

my $dbh = DBI->connect( @connect_info );
isa_ok $dbh, 'DBI::db';

my $sql = 'SELECT 1';
test_query( $sql );
test_query( $sql );

sub test_query {
    my ($sql) = @_;

    my $sth = $dbh->prepare_cached( $sql );
    isa_ok $sth, 'DBI::st';

    my $r = $sth->execute();
    {
        no warnings 'uninitialized';
        ok defined( $r ), "defined: '$r'";
    }

    ok $sth->finish(), '$sth->finish';

    return;
}

done_testing;
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I've obscured the actual connect info. This is what the output looks like:

ok 1 - The object isa DBI::db
ok 2 - The object isa DBI::st
ok 3 - defined: '-1'
ok 4 - $sth->finish
ok 5 - The object isa DBI::st
not ok 6 - defined: ''
#   Failed test 'defined: '''
#   at t/dbi-bug-pm.t line 35.
ok 7 - $sth->finish
1..7
# Looks like you failed 1 test of 7.
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Note that if you uncomment the SQLite connect info, it works fine. That's why I think this is a problem with my database or driver. You can see a run with SQLite below.

ok 1 - The object isa DBI::db
ok 2 - The object isa DBI::st
ok 3 - defined: '0E0'
ok 4 - $sth->finish
ok 5 - The object isa DBI::st
ok 6 - defined: '0E0'
ok 7 - $sth->finish
1..7
[download]

Note also that if I disconnect from the database and reconnect between the queries, they work, but I don't think disconnecting from the database after every query is a very good workaround.

I'd be happy with a workaround for this issue. If I could stick some code in every ResultSet so that it avoids the problem until it's fixed elsewhere, that would be fine with me, but I don't even understand what's going wrong. I'm asking here to see if someone is familiar with it and what it means.

My searching for the issue online turned up a thread from about a year ago (http://lists.scsys.co.uk/pipermail/dbix-class/2012-June/010553.html). If there's an answer in there, I failed to comprehend it.

Any help would be appreciated. Thank you.

In reply to My MSSQL query fails the second time. by kyle

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