Calling db in a function - eloquent

Question

I'm trying to use a function that I wrote inside my routes.php file:
the function is this:
function userScore($uid) {
$db = $app->get('db');
//calcolo punteggio totale
$query_punti = $db->table('prodotti_sounding')
->where('id_utente', $uid)
->select('punti')
->get();
$totale_punti = 0;
foreach($query_punti as $item) {
$totale_punti += $item->punti;
}
}
it returns this error:
Slim Application Error The application could not run because of the
following error:
Type: Error Message: Call to a member function get() on null
where am I wrong?
EDIT
my relevant code in routes.php after the first answer is:
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Message\ResponseInterface;
use Illuminate\Database\Connection;
use Slim\Http\UploadedFile;
use Illuminate\Support\Facades\DB as DB;
$container = $app->getContainer();
$app->post('/sendbarcode', function ($request, $response){
/* parametri barcode */
/** #var Container $this */
/** #var Connection $db */
$barcode = $request->getParsedBodyParam('barcode');
$id_utente = $request->getParsedBodyParam('id_utente');
$db = $this->get('db');
// prepare data for json
$array['itacheck'] = 0;
if(checkbarcode($barcode) == 1 ) {
$array['it_check'] = 1;
$array['punti'] = 25;
$array['totalepunti'] = userScore($id_utente);
}
$array['barcode'] = $rows;
if(count($rows) > 0){
return $response->withJson($array, 200, JSON_UNESCAPED_UNICODE|JSON_UNESCAPED_SLASHES|JSON_UNESCAPED_LINE_TERMINATORS);
}
});
function userScore($uid) {
//calcolo punteggio totale in base alle segnalazioni pregresse
$query_punti = DB::table('prodotti_sounding')
->where('id_utente', $uid)
->select('punti')
->get();
// check total points
$totale_punti = 0;
foreach($query_punti as $item) {
$totale_punti += $item->punti;
}
}

Answer 1

Error becomes $db = $app->get('db');, because you not defained $app variable. Instaed of you can use this
//calcolo punteggio totale
$query_punti = DB::table('prodotti_sounding')
->where('id_utente', $uid)
->select('punti')
->get();
DB full class name is \Illuminate\Support\Facades\DB
Edit
That case add $app attribute in function argument
function userScore($uid, $app) {
$db = $app->get('db');