Spring Boot JPA 忽略 OneToMany 双向的延迟加载

Question

我正在使用 springboot（spring-boot-starter-parent 2.3.0 版本）和 Jpa。我有 User 类，它是父类，UserEmails 是子实体。

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);
       });
}
}

UserRoles 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，即使我在关系的双方都使用 fetch 类型作为惰性，但当我调用 getUserById 或 getAllUsers 时，jpa 也会加载用户电子邮件。

用户服务实现

@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;
    }
} 

用户DAO

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

    public User findById(int id);

}

Answer 1

是的，它可能会发生，如果您使用持久对象（在您的实例中为 User 的对象）作为控制器之一中的返回值（例如 REST URL /user/{id} 处的 ResponseEntity<User> getUser(Long id)），就会发生这种情况 如果您有类似的 REST 控制器，则会发生 UserEmails 的延迟获取。 这种惰性获取基本上会发生在控制器的返回语句中。

你有两种可能：

1. 定义DTO对象，例如UserDTO，mapper在User和UserDTO之间进行映射 的

2. 在User 类中使用@JsonIgnoreProperties 和@JsonProperty 等其他注解：

        @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);
           });
         }}
   

   .