How use ModelObject->save($entityObject) well?

Model has a snowflakeId as primaryKey.  
in ver 4.2.1  can not allow primaryKey in $allowedFields array.

How can use Entity and Model correctly ?

PHP Code:

$userArray = [
    'key' => snowFlakeId(), //primaryKey
    'userName' => 'XXXX',
];

$this->userModel->save(new \App\Entities\UserEntity($userArray));