Spring Boot JPA忽略OneToMany双向的延迟加载

Question

我与Jpa一起使用springboot（spring-boot-starter-父2.3.0版本）。我有作为父实体的User类和作为子实体的UserEmails。

用户实体

@Entity
@Table(name = "user")
public class User extends BaseEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @NotEmpty(message = "Name cannot be empty")
    @Column(name = "name")
    private String name;

    @OneToMany(mappedBy = "user",fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JsonManagedReference
    private List<UserEmails> userEmails = new ArrayList<UserEmails>();
 
    //setters and getters

     public void setUserEmails(List<UserEmails> userEmails) {
       this.userEmails= userEmails;
       this.userEmails.forEach(userEmail->{
         userEmail.setUser(this);
       });
}
}

用户角色实体

@Entity
@Table(name = "user_emails")
public class UserEmails extends BaseEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    
    @Column(name="email")
    private String email;

    @JsonBackReference
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id" , referencedColumnName = "id", nullable=true)
    private User user;

    //getters and setters
}

问题是，即使我在关系的两边都使用fetch类型作为懒惰，但当我调用getUserById或getAllUsers时，jpa也会加载用户电子邮件。

用户服务简介

@Service
public class UserServiceImpl extends BaseServiceImpl implements UserService {

    private static final Logger logger = LoggerFactory.getLogger(UserServiceImpl.class);

    @Autowired
    UserDAO userDAO;

   @Override
    public User getUserById(int id) {
        logger.info("Executing getUserById() in user service");
        User user = null;
        
        try {
            user = userDAO.findById(id);
        } catch (DataAccessException e) {
            String message = "Some message"
            throw new Exception(message, e);
        }

        if (user == null) {
              String message = "Some message"
              throw new ResourceNotFoundException(message);
        }
        return user;
    }
} 

UserDAO

@Repository
public interface UserDAO extends JpaRepository<User, Long>{
    

    public User findById(int id);

}

Answer 1

是的，它可能会发生，如果您在一个控制器（例如＜code＞ResponseEntity）中使用持久化对象（在您的例子中是实例用户的对象）作为返回值，则会发生这种情况

你有两种可能:

> < li>

定义DTO对象，例如UserDTO，以及在的用户和UserDTO之间进行映射的映射器

要在用户类中使用其他注释，如@jsonignoreperties和@JsonProperty：

     @Entity 
     @Table(name = "user") 
     @JsonIgnoreProperties({"userEmails"})
     public class User extends BaseEntity {

     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     private int id;

     @NotEmpty(message = "Name cannot be empty")
     @Column(name = "name")
     private String name;

     @OneToMany(mappedBy = "user",fetch = FetchType.LAZY, cascade = CascadeType.ALL)
     @JsonManagedReference
     @JsonProperty("userEmails")
     private List<UserEmails> userEmails = new ArrayList<UserEmails>();

     //setters and getters

      public void setUserEmails(List<UserEmails> userEmails) {
        this.userEmails= userEmails;
        this.userEmails.forEach(userEmail->{
          userEmail.setUser(this);
        });
      }}

.