I changed a few things and did some progress (I think)...

First, rename the whole thing from Lib to MyLib and reread the doc

My +folders are now

 run.pl
 my_lib.conf
 +templates
     common_js.html.ep
     invtot.html.ep
     libmap.html.ep
     +layouts
        default.html.ep
  +public
      index.html
      some .js files
  +lib
     MyLib.pm
     +MyLib
      Invtot.pm
         +Controller
              Invtot.pm
[download]

I have the post action starting until it crashes on the line trying to fetch the database handler which is get from startup in package MyLib::Invtot. The whole file is

package MyLib::Invtot;
use Mojo::Base 'Mojolicious';

sub startup {
    my $app    = shift;
    my $config = $app->config;
     $app->log->debug("connecting...");
    $app->plugin(
        'Database',
        {   dsn      => 'dbi:mysql:host=mysql.unifr.ch:dbname=dokpe_i0
+1',
            username => $config->{username},
            password => $config->{password},
            options  => {
                'pg_enable_utf8' => 1,
                AutoCommit       => 1,
                PrintError       => 0,
                RaiseError       => 1
            },
           helper => 'db',
        }
    );
}
1;
[download]

and the call to helper => db should make it accessible to the controller in MyLib/Controller/Invtot. That's not the case and I'm not even sure it's called at all. How can I make sure the connection is made the first time the invtot page is load and how can I then retrieve the database connection in the controller ?

Thanks