How to hook after DBI reconnect - perl

Question

I deal with a module which provides abstraction over DBI which automatically reconnects. I need to perform some actions after `DBI->connect.
Is there a way to add a hook there without modifying this module? I don't have luck finding it in the documentation. Did I miss something?

Answer 1

The DBI doc has a chapter about subclassing which mentions a $dbh->connected method that does nothing. It seems to be exactly what you want.
When subclassing is being used then, after a successful new connect, the DBI->connect method automatically calls:
$dbh->connected($dsn, $user, $pass, \%attr);
I have not tried that, but it might work by just monkey-patching this connected method into DBI directly without subclassing anything. In connect there is definitely a call to connected.
But I am not sure where to patch that in. Possibly into the driver. A quick grep of the cpan shows that only two drivers included in the DBI dist include this. DBD::Gofer and DBD::Proxy, but that one is empty. In both of them it's in the DBD::<drivername>::db package.
Let's assume you are doing MySQL, then you'd go and hook it into your driver. Either by subclassing and using that driver, or by simply monkey-patching it in.
*DBD::mysql::db::connected = sub {
my ($dbh, dsn, $user, $pass, $attr, $old_driver) = #_;
warn 'Connected!';
}
This should work the same with other drivers, unless they have their own connected. In that case, you should probably wrap it manually or use something like Class::Method::Modifiers's around to wrap it to make sure the original behavior stays intact.
You also have the actual connected $dbh at this point, so you can go rummaging around in the database in connected if you want.
Of course this would give you the callback after every connect. If you wanted to only get the reconnects, you could create a closure over a lexical variable that counts the connections and skip the very first one.
{
my $connection_counter;
*DBD::mysql::db::connected = sub {
my ($dbh, dsn, $user, $pass, $attr, $old_driver) = #_;
return unless $connection_counter++; # skip first connection
warn 'Connected!';
}
}
Please note that I have not tested any of this.

Answer 2

While I must say I have not tried this; I found this article
http://justatheory.com/computers/databases/postgresql/execute-on-select.html
where #theory writes about an option to leverage DBI to run code whenever something happens - like connect. Hope it helps!