Mojolicious and DBI handles


From we find this bit of code:

sub startup {
  my $app = shift;

  my ($user, $pass);
  # read $user and $pass from config file
  (ref $app)->attr(db => sub {
                 $user, $pass)

The concept is that Morbo, or Starman, or whatever PSGI server is running your program, can use any kind of forking, but each instance of your program will execute the startup code and create its own database handle.

Some of the code is not too obvious:

And here's how you get the data back out:

  $app->get('/test')->to(cb =>
               my $self = shift;
               $Data::Dumper::Indent = 1;
               $self->render( 'text' => "TEST: ATTR of foo" . $self->app->foo .
                    "\n<pre>\n" . Dumper($self) . "</pre>" );

It's really a better idea to use DBIx::Connector anyway, but the startup attribute trick might come in handy elsewhere. One note on DBIX::Connector − Under the heading, Execution Methods we see the code:

  <span class="sh_variable">$conn</span><span class="sh_symbol">-></span><span class="sh_function">run</span><span class="sh_symbol">(</span><span class="sh_keyword">sub</span> <span class="sh_cbracket">{</span> <span class="sh_variable">$_</span><span class="sh_symbol">-></span><span class="sh_keyword">do</span><span class="sh_symbol">(</span><span class="sh_variable">$query</span><span class="sh_symbol">)</span> <span class="sh_cbracket">}</span><span class="sh_symbol">);</span>

It is not documented, but by reading the source (let's hear it for free software!) what happens is that $_ is set, via the «local» keyword, to temporarily be the database handle (dbh) of the connection within execution of the code reference.

Thanks to mst and others on #perl for the assistance.