實際上，有很多關于這個的帖子。但即使我檢查了那些，仍然找不到問題。DBC類protected function connect(){    $dns = "mysql:host=" . $this->server . ";dbname=" . $this->database;    $pdo = new PDO($dns, $this->username, $this->password);    $pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);    return $pdo;}并插入函數。public function insert_row($created_at){    $sql = "INSERT INTO empty_rows (created_at) VALUES (?)";    $stmt = $this->connect()->prepare($sql);    $stmt->execute([$created_at]);      $id = $this->connect()->lastInsertId();    echo $id;}我認為它應該返回最后插入的 Id 但是，它只返回 0。我在這里缺少什么？