private function assignImage($field, $filePath, $model)
{
$file = new File();
$file->fromFile($filePath);
if (!is_null($model->{$field}) && strtotime($model->{$field}->updated_at) < filemtime($filePath)) {
echo "Update " . $field . " by file " . $file->getFilename() . "\n";
$model->{$field}->delete();
$model->{$field}()->save($file);
}
}