Re: using callbacks with connect_cached

[David E. Wheeler]

On Aug 24, 2013, at 9:40 PM, Vincent Veyron <vv.li...@wanadoo.fr> wrote:

> Not quite : I thought connected_cache.new would enable me to set the
> correct datestyle once for a cached connection, and then be cached with
> it, but we've seen that won't work.
> 
> Using the connected callback would do a 'set datestyle to xyz' for each
> connection, even if cached. I realize it's no big deal (.5ms on my lowly
> Atom processor), but every little bit helps, as I'm sure you know. 
> 
> So I now set the datestyle when the user logs in (hence once, with
> $dbh->do('SET datestyle TO xyz'), and the database handle is cached and
> reused as is.

You can also use a private attribute in connect_cached.new to tell the 
connected callback to do its thing:


my $cb = {
    'connect_cached.new' => sub {
        $_[4]->{private_is_new} = 1;
        return;
    },
    connected => sub {
        my $dbh = shift;
        warn "connected\n" if delete $dbh->{private_is_new};
        return;
    }
};

for (1..3) {
    DBI->connect_cached('dbi:SQLite:', '', '', {
        PrintError => 0,
        RaiseError => 1,
        AutoCommit => 1,
        Callbacks  => $cb,
    });
}

This emits "connected" only once.

Best,

David