TalkPHP - num rows

hello im new here and im getting this error
Fatal error: Call to a member function execute() on a non-object in PATH......

im using this class to get the num rows please correct me

PHP Code:


		
			
public function prepareDB($query = NULL) {
        $prepare = $this->mysqli->prepare($query);
        return $prepare;
        }
    
    public function numDB($query = NULL) {
        $this->stmt = $this->prepareDB($query);
        $this->stmt->execute();
        $this->stmt->store_result();
        $num = $this->stmt->num_rows;
        $this->stmt->close();
        return $num;
        }

PHP Code:


		
			
$query = "SELECT * WHERE smthng='value'";
$num = $Database->numDB($query);

echo $num;

thx.