java - DDD : is accessing repository from aggregate root considered bad practice?

Question

我读到从聚合根访问存储库被认为是不好的做法。如果是，请考虑以下示例:

class User {
   private String username;
   public void changeUsername(String newUsrname) {
     // How will I persist username to database if I don't have access to repository from aggregate root?
     ...
   }
}

如果我无权访问存储库，如何将用户名保留到数据库来自聚合根？

我是这样看的:

class User {
    private String username;
    private UserRepository userRepository;
    public User(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public void changeUserName(String newUsername) {
       this.username = newUserName;
       userRepository.save(this); 
    }
}

或者我错过了 DDD 概念中的某些内容？

Answer 1

How will I persist username to database if I don't have access to repository from aggregate root?

当前的实践通常在应用程序组件中处理 I/O，而不是在域模型中。

Application {
    void when(ChangeUserName command) {
        User user = this.userRepository.getUserById(command.userId);
        user.changeName(command.name);
        this.userRepository.save(user);
    }
}

推荐阅读:Vladimir Khorikov关于领域模型隔离。