PHP DateTime类很奇怪

Question

Consider the following block of code, I've passed a string to the DateTime constructor. Now in line 3 I change the contents of the variable i've used, I get an error from line 2?

Why would I get an error from the constructor in line 2 from what I've done in line 3?

I've also tried clone on the $user object then having one object for the datetime and another for altering its contents. It still doesn't work, gives me the exact same error.

$userDatetime = "".$user->user_api_rolling_datetime;

$rollingHourEndsAt = new \DateTime($userDatetime);

$user->user_api_rolling_datetime = new Expression('NOW()');

The Error:

DateTime::__construct(): Failed to parse time string (NOW()) at position 3 ((): Unexpected character

Answer 1

Although I'm unsure what was causing the above issue. The following workaround worked:

$rollingHourEndsAt = new \DateTime();
$rollingHourEndsAt->setTimestamp(strtotime($user->user_api_rolling_datetime));
$user->user_api_rolling_datetime = new Expression('NOW()');