java - Spring 中的 LazyInitializationException 与 JPA 实体

Question

我想在 JPA 实体上从 EAGER 获取切换到 LAZY 获取，但随后出现错误。我已经尝试了很多解决方案，并且一直在寻找有效的解决方案 - 找不到任何适用于 Google 的解决方案...而且我也不希望该实体加入 fetch。

错误:org.hibernate.LazyInitializationException:无法延迟初始化角色集合:package.User.wallets，无法初始化代理 - 无 session

网络 Controller 文件:

@Controller
public class AppController {

    @GetMapping("app/")
    public ModelAndView app() {

        ModelAndView mv = new ModelAndView();
        mv.setViewName("app/index");

        User user = (User) SecurityContextHolder.getContext().getAuthentication().getPrincipal();

        List<Wallet> wallets = user.getWallets(); // error on this line
        mv.addObject("wallets", wallets);

        return mv;
    }
}

用户文件:

@Entity
public class User {

    @Id
    @GeneratedValue
    @Type(type="uuid-char")
    private UUID id;

    @Column(nullable = false)
    private String email;

    @Column(nullable = false)
    private String firstName;

    @Column(nullable = false)
    private String lastName;

    @Column(nullable = false)
    private String password;

    // FetchType.EAGER solves the error, but I can't have EAGER due to performance issues.
    @OneToMany(mappedBy="user", fetch = FetchType.LAZY)
    @Fetch(value = FetchMode.SUBSELECT)
    private List<Wallet> wallets;

    // ** getters and setters **

}

@Repository
public interface UserRepo extends JpaRepository<User, UUID> {

    Optional<User> findByEmail(String email);

}

钱包文件:

@Entity
public class Wallet {

    @Id
    @GeneratedValue
    @Type(type="uuid-char")
    private UUID id;

    @ManyToOne
    @JoinColumn(name="user_id", nullable=false)
    private User user;

    @OneToOne
    @JoinColumn(name="currency_id", nullable=false)
    private Currency currency;

    @Column(nullable = false)
    private double balance;

    // ** getters and setters **

}

@Repository
public interface WalletRepo extends JpaRepository<Wallet, UUID> {

    Optional<Wallet> findByUserAndCurrency(User user, Currency currency);

}

感谢您阅读所有这些，我非常感谢您的回复。

Answer 1

问题的根源:

默认情况下，hibernate 延迟加载集合(关系)，这意味着每当您在代码中使用集合时，hibernate 都会从数据库中获取集合，现在的问题是您正在 Controller 中获取集合(其中 JPA session 已关闭) )。这是导致异常的代码行(您正在加载评论集合):

List<Wallet> wallets = user.getWallets();

解决方案

您的用户实体中有此

 @OneToMany(mappedBy="user", fetch = FetchType.LAZY)
    @Fetch(value = FetchMode.SUBSELECT)
    private List<Wallet> wallets;

用这个

@OneToMany(fetch = FetchType.EAGER, mappedBy = "user", cascade = CascadeType.ALL)
private List<Wallet> wallets;

Collections are lazy-loaded by default

更新的解决方案

这种特殊情况可以通过在 User 中添加 toString() 来重新定义 Lombok toString() 来解决

保留您的fetchType.LAZY而不是fetchType.EAGER并且将 toString 方法添加到您的用户实体

@Override
public String toString() {
        return "User [id=" + id + ", email=" + email+ ", firstName=" + firstName+ ", lastName=" + lastName + ", password=" + password+ "]";
    }

并向您添加钱包实体:

  @ManyToOne(fetch=FetchType.EAGER)
  @JoinColumn(name="user_id", nullable=false)
  private User user;

尝试将 @Transactional 添加到您的 Controller