java - Spring Boot 和 fetchType=Lazy

Question

我的 Spring Boot 应用程序中存在延迟初始化问题。我有一个带有惰性字段 Role 的实体，并且在我的 Spring Security (UserDetailsS​​ervice) 方法中有 LazyInitializationException ，但在 Controller 中没问题。你能向我解释一下 Spring Boot 如何与 fetch = FetchType.LAZY 配合使用吗？为什么它不能在 Spring Security UserDetailsS​​ervice 中工作并且在 Controller 方法中工作？我没有找到任何关于此的指南。谢谢!

Spring 启动:

@SpringBootApplication
public class App {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(App.class, args);
    }
}

实体:

@Entity
@Table(name = "users")
@Getter
@Setter
@NoArgsConstructor
public class Users {
    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "Users_Role", joinColumns = @JoinColumn(name = "User_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(name = "role_id", referencedColumnName = "id"))
    private Set<Role> roles = new HashSet<Role>();
}

我的服务:

@Transactional(readOnly = true)//does not matter
 public Users getUserByLogin(String login) {
        return usersRepository.findOneByLogin(login);
    }

    @Transactional(readOnly = true)
    public Users getUserByLoginWithRoles(String login) {
        Users oneByLogin = usersRepository.findOneByLogin(login);
        logger.debug("User was initialize with Roles: " + oneByLogin.getRoles().size()); // force initialize of roles and it works!
        return oneByLogin;
    }

   @Transactional(readOnly = true)//does not matter
    public Users testGetUser() {
        Users oneByLogin = usersRepository.getOne(1L);
        return oneByLogin;
    }

    @Transactional(readOnly = true)//does not matter
    public Users testFindUser() {
        Users oneByLogin = usersRepository.findOne(1L);
        return oneByLogin;
    }

我有 Spring Security UserDetailsS​​ervice:

@Service
    public class UserDetailsServiceImpl implements UserDetailsService {

    @Autowired
    private Services services;

    @Override
    public UserDetails loadUserByUsername(String login) throws UsernameNotFoundException {
        Users user;
        Users userFetchedViaGet = services.testGetUser();
        Users userFetchedViaCustomMethod = services.getUserByLogin(login);
        Users userFetchedViaFind = services.testFindUser();
        Users userFetchedWithRoles = services.getUserByLoginWithRoles(login);
        try {
            userFetchedViaGet.getRoles().add(new Role("test"));
        } catch (Exception e) {
            e.printStackTrace();//LazyInitializationException: failed to lazily initialize a collection of role: , could not initialize proxy - no Session
        }
        try {
            userFetchedViaCustomMethod.getRoles().add(new Role("test"));
        } catch (Exception e) {
            e.printStackTrace();//LazyInitializationException: failed to lazily initialize a collection of role: , could not initialize proxy - no Session
        }
        try {
            userFetchedViaFind.getRoles().add(new Role("test")); //LazyInitializationException: failed to lazily initialize a collection of role: , could not initialize proxy - no Session
        } catch (Exception e) {
            e.printStackTrace();
        }
        //some code
        }
    }

和我的 Controller (所有方法都有效!但是必须发生异常，因为没有 session 和延迟获取类型):

@RequestMapping(value = "/test", method = RequestMethod.GET)
    public String test() {      
        Users userFetchedViaGet = services.testGetUser();
        Users userFetchedViaCustomMethod = services.getUserByLogin("ADMIN");
        Users userFetchedViaFind = services.testFindUser();
        Users userFetchedWithRoles = services.getUserByLoginWithRoles("ADMIN");
        try {
            userFetchedViaGet.getRoles().add(new Role("test"));
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            userFetchedViaCustomMethod.getRoles().add(new Role("test"));
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            userFetchedViaFind.getRoles().add(new Role("test"));
        } catch (Exception e) {
            e.printStackTrace();
        }
        //some code
    }

Answer 1

您需要一个事务来包装整个事物 - 在您的外观上 - test() 方法才能使其工作，但这并不是一个好的实践。

解决方法是让您的服务将 api 方法包装在事务中，并返回一个完全加载的对象 - 包含所有子节点。该对象可以是一个从 Users 类构造的简单 bean，从对象构建的 HashMap ，甚至是您想要从其余调用返回的字符串。