Groups | Search | Server Info | Login | Register

Groups > perl.dbi.users > #3366

Re: Need help with an unexpected behaviour

Show all headers | View raw

On Fri, Jan 26, 2018 at 04:47:35PM +0100, Andreas Mock wrote:
> Hi all,
> 
>   9 my %attr = (
>  10     'AutoCommit' => 1,
>  11     'RaiseError' => 1,

>  35 sub doit {
>  36     my $dbh = shift;
>  37
>  38     local $dbh->{'AutoCommit'} = 1;
>  39
>  40     $dbh->begin_work;
>  41     $dbh->do("insert into mca_rb_test values ('short')");
>  42     $dbh->do("insert into mca_rb_test values
> ('looooooooooooooooooooooooooooooooooooooooooooooooooong')");
>  43     $dbh->commit;

> Whithout line 38 I get what I expect. [...]

> BUT: As soon as I have line 38 in there, which shouldn't change
> the initially set 'AutoCommit', the first insert is commited
> to the database even the exeption is raised in the opened
> transaction.

That seems like a driver bug at first sight.

While "local $dbh->{'AutoCommit'} = 1;" looks like a simple
hash assignment there's a lot going on behind the scenes.
($dbh is a ref to a tied hash so a STORE method gets called
to handle the assignment.)

While it doesn't "change" the AutoCommit setting, since it's already
enabled, the "local" does cause Perl to arrange to execute
$dbh->{'AutoCommit'} = 1 when the scope exits.

Both the initial assignment and the re-setting assignment may have side
effects.

> Can someone explain what is happening behind the scenes or
> give a pointer to some helpful documentation which I have overlooked?

The DBI (and most drivers) have extensive tracing built in.
The trace output is often very helpful to see what's really happening.
See https://metacpan.org/pod/DBI#TRACING

It'll show you the effect of the local AutoCommit assignment and
re-setting assignment at scope-exit.

Tim.

Back to perl.dbi.users | Previous | Next — Previous in thread | Next in thread | Find similar

Thread

Need help with an unexpected behaviour andreas.mock@web.de ("Andreas Mock") - 2018-01-26 16:47 +0100
  Re: Need help with an unexpected behaviour Tim.Bunce@pobox.com (Tim Bunce) - 2018-01-28 13:43 +0000
    AW: Need help with an unexpected behaviour andreas.mock@web.de ("Andreas Mock") - 2018-01-28 15:12 +0100

csiph-web