为什么新增数据的created_at没有自动维护

class Student extends Model

{

protected $table = 'student';

public $timestamps = true;

protected function getDateFromat()

{

return time();

}

protected function asDateTime($val)

{

return $val;

}

}

public function save(Request $request)

{

$data = $request->input('Student');

//var_dump($data);

$students = new Student();

$students->name = $data['name'];

$students->age = $data['age'];

$students->sex = $data['sex'];

//$student->save();

if($students->save()){

return redirect('student/index');

}else{

return redirect()->back();

}

}