使用PDO连接到数据库，执行查询并在一行中获取结果

Use PDO to connect to database, execute query and fetch results in one line

$query = "SELECT * FROM user WHERE id = 1;";
$stmt = $this->openDb()->prepare($query);
$stmt->execute();
$rows = $stmt->fetchAll(PDO::FETCH_ASSOC);

为什么这个代码不起作用，并给我错误Fatal error: Call to a member function fetchAll() on a non-object in

$result_set = $this->openDb()->prepare("SELECT * FROM user WHERE id = 1;")->execute()->fetchAll(PDO::FETCH_ASSOC);

$stmt->execute（）；不返回对象，而是返回布尔值。http://www.php.net/manual/de/mysqli-stmt.execute.php