Call to a member function format() on string 或者 Call to a member function format() on integer
解决办法如下（最好都加上）：
public function freshTimestamp() {
return time();
}
public function fromDateTime($value)
{
return $value;
}
public function getDateFormat()
{
return time();
}
protected function asDateTime($value)
{
return $value;
}
