Laravel 5.1 在表单请求验证前修改输入

When I set $this->start_dt input field to 2016-02-06 12:00:00 and $this->end_dt to 2016-02-06 13:00:00 I still get validation error "end_dt must be after start_dt". Which means the input request values aren't getting changed when you update $this->start_dt and $this->end_dt inside the rules() function.

public function rules()
{
    if ($this->start_dt){
        $this->start_dt = Carbon::createFromFormat('d M Y H:i:s', $this->start_dt . ' ' . $this->start_hr . ':'. $this->start_min . ':00');
    }

    if ($this->end_dt){
        $this->end_dt = Carbon::createFromFormat('d M Y H:i:s', $this->end_dt . ' ' . $this->end_hr . ':'. $this->end_min . ':00');
    }

    return [
        'start_dt' => 'required|date|after:yesterday',
        'end_dt' => 'required|date|after:start_dt|before:' . Carbon::parse($this->start_dt)->addDays(30)            
    ];
}

注意: start_dt 和 end_dt 是日期选择器字段，start_hr、start_min 是下拉字段.因此，我需要通过组合所有字段来创建一个日期时间，以便我可以进行比较.

/**
 * Modify the input values
 *
 * @return void
 */
protected function prepareForValidation() {

    // get the input
    $input = array_map('trim', $this->all());

    // check newsletter
    if (!isset($input['newsletter'])) {
        $input['newsletter'] = false;
    }

    // replace old input with new input
    $this->replace($input);
}