EclipseLink，可在事务外部访问懒惰的获取集合 [英] EclipseLink, lazy fetch collection is accessible outside of transaction

问题描述

我有一个名为User的实体，该实体具有以下名为roles的字段:

I have an entity named User which has the following field called roles:

@ManyToMany
@JoinTable(
        name = "user_role",
        joinColumns = {@JoinColumn(name = "user_id", nullable = false)},
        inverseJoinColumns = {@JoinColumn(name = "role_id", nullable = false)}
)
private List<Role> roles;

我使用服务方法加载User，并且该服务方法包装在事务(JTA)中.调用服务方法并检索User之后，我在用于加载User实体的事务之外访问此role字段.我期望得到一个错误，因为eclipselink文档指出，默认情况下，ManyToMany关联的特征类型为

I load the User via the use of a service method and the service method is wrapped in a transaction (JTA). After calling the service method and retrieving the User, I access this role field outside of the transaction that was used to load the User entity. I was expecting to get an error because the eclipselink documentation states that, by default, the fechtype for a ManyToMany association is lazy. This tells me that when the User entity was loaded in the service method, the roles should not be automatically loaded.

为什么我可以在交易之外访问roles?为什么看起来roles是急切地取而代之的，而不是懒惰的?

Why was I able to access the roles outside of the transaction? Why does it seem like the roles were fetched eagerly instead of lazy?

这是加载用户的服务类(我删除了一些与问题无关的代码):

Here is the service class which loads the user (I've removed some code not relevant to the question):

@Service
@Transactional(rollbackFor = ServiceException.class)
public class UserServiceImpl implements UserService {

    @Autowired(required = true)
    private UserRepository userRepository;


    @Override
    public User authenticate(String username, String password) throws ServiceException {
        //Get the user
        List<User> users = userRepository.findByUsername(username);

        if (users == null || users.isEmpty() || users.size() > 1) {
            return null;
        }

        User user = users.get(0);
        String hash = getHash(password, user.getSalt());

        return StringUtils.equals(hash, user.getPassword()) ? user : null;
    }
}

推荐答案

只要上下文仍然可用，EclipseLink即可获取惰性关系，如下所述:

EclipseLink allows fetching lazy relationships as long as the context is still available as described here: https://forums.oracle.com/forums/thread.jspa?messageID=1706796

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