java - JPA Spring 忽略 @Transacational 内的延迟加载

Question

我有一个 spring 服务类，我在其中通过 CRUD 加载 JPA 对象(目标)。该目标类具有设置为延迟加载的一对多映射。

我想在用@Transactional注释的Spring服务方法中查询这个对象，并避免加载子对象。

当我执行以下代码时，所有子数据都会被加载，并且惰性会被忽略。

        @Override
        @Transactional
        public boolean changeState(boolean enabled, final EventType eventType, final String deviceSerialNumber) {
            final UniqueUser user = userService.getUser();
            final Target target = targetRepository.findEventsByUserIdAndTenantIdAndTargetDeviceId(user.getUserId(), user.getTenantId(), deviceSerialNumber);
//here everything gets loaded
            if (target == null) {
                return false;
            }
            final List<EventHistory> events = target.getEvents().stream()
                    .filter(event -> event.getEventType() == eventType)
                    .filter(event -> event.isActive() != enabled)
                    .collect(Collectors.toList());
            events.forEach(event -> event.setActive(enabled));
            if (events.isEmpty()) {
                return false;
            }
            return true;
        }

映射:

    @ToString
    @Entity
    @Table(name = "target")
    public class Target {

        @Id
        @GeneratedValue(generator = "uuid")
        @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
        @Column(name = "id", unique = true)
        private UUID id;

        @Column(name = "user_id")
        private String userId;

        @Column(name = "tenant_id")
        private String tenantId;

        @Column(name = "target_device_id")
        private String targetDeviceId;

        @Column(name = "target_type")
        private TargetType targetType;

        @OneToMany(mappedBy = "target", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
        @JsonManagedReference
        private List<EventHistory> events = new ArrayList<>();

        public void addEvents(EventHistory event) {
            events.add(event);
            event.setTarget(this);
        }

    }

    @Entity
    @Data
    @Table(name = "event_history")
    public class EventHistory {

        @Id
        @GeneratedValue(generator = "uuid")
        @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
        @Column(name = "id", unique = true)
        private UUID id;

        @Column(name = "active")
        private boolean active;


        @OneToMany(mappedBy = "event", cascade = CascadeType.ALL, orphanRemoval = true)
        @JsonManagedReference
        private List<EventTimestamp> timestamps = new ArrayList<>();

        @ManyToOne(optional = false, cascade = CascadeType.ALL, fetch = FetchType.LAZY)
        @JoinColumn(name = "target_id", nullable = false)
        @OnDelete(action = OnDeleteAction.CASCADE)
        @JsonBackReference
        private Target target;

        public void addTimestamps(EventTimestamp eventTimestamp) {
            timestamps.add(eventTimestamp);
            eventTimestamp.setEvent(this);
        }

    }

    @Entity
    @Data
    @Table(name = "event_timestamp")
    public class EventTimestamp {
        @Id
        @GeneratedValue(generator = "uuid")
        @GenericGenerator(name = "uuid", strategy = "org.hibernate.id.UUIDGenerator")
        @Column(name = "id", unique = true)
        private UUID id;


        @Column(name = "due_timestamp")
        private Timestamp dueTimestamp;

        @Column(name = "period")
        private String period;

        @ManyToOne(fetch = FetchType.LAZY)
        @JoinColumn(name = "event_id", nullable = false)
        @JsonBackReference
        private EventHistory event;

所以我的问题是如何在事务注释函数内保持延迟加载？

Answer 1

我的第一个假设是错误的，即根本原因是错误地实现了存储库功能。真正的问题是 @ToString 注释。这将一对多事件集合添加到 toString()。在事务内部并访问对象时，调用 toString 并加载集合。

解决方案是通过 toString 排除集合。

@OneToMany(mappedBy = "target", cascade = CascadeType.ALL, orphanRemoval = true)
@ToString.Exclude
private List<EventHistory> events;