$connection = mysqli_connect($servername,$username,$password,$dbname) or die("Error connecting" . mysqli_error($connection));
    $sql = "select pID,pName,pDesc,pPrice from CommunityStoreProducts";
    $result = mysqli_query($connection, $sql) or die("Error in Selecting " . mysqli_error($connection));
    $emparray = array();
    while($row = mysqli_fetch_assoc($result))
    {
        $emparray[] = $row;
    }
    $fp = fopen('application/themes/theme/json.json', 'w');
    fwrite($fp, json_encode($emparray,JSON_NUMERIC_CHECK));
    fclose($fp);
    mysqli_close($connection);

$app = \Concrete\Core\Support\Facade\Facade::getFacadeApplication();
$db = $app->make(Connection::class)->connection();
or 
 $db = \Database::connection();