gistfile1.pl

# somewhere the app has a 'mango' attribute that was set up like this:
# $app->attr(mango => sub { Mango->new('localhost') });
sub some_action {
    my $self = shift;
    
    $self->render_later;
    $self->mango->db('mydb')->collection('baz')->find_one({ _id => $self->req->param('id') } => sub {
        my ($coll, $err, $doc) = (@_);
        if($err) {
            $self->render(json => { error => $err });
        } elsif($doc) {
            $self->render(json => $doc);
        } else {
            $self->ua->get('http://myfallbackapi.com/?id=' . $self->req->param('id') => sub {
                my ($ua, $tx) = (@_);
                if(my $res = $tx->success) {
                    # pretend we got some odd data that got munged into $res_data here
                    $self->mango->db('mydb')->collection('baz')->insert($res_data => sub {
                        $self->render(json => $res_data);
                    });
                } else {
                    $self->render(json => { error => 'oops...' });
                }
            });
        }
    });