Spring-Data 中子对象不与父对象一起获取

Question

我对 Hibernate 很陌生，我已经在父对象和子对象之间设置了 @OneToMany 双向关系，并期望当我将所有内容保留在数据库中时，将父对象设置为子对象（因为子对象是关系的所有者）当我使用 ORM 获取父对象时，我希望也获取子对象，但作为回报，我看到零个子对象。据我在互联网上阅读的内容了解，当我将子对象保留为与父对象的关系的所有者时，完整的 ORM 应该发挥根据预定义关系映射连接两个对象的魔力。此信息正确吗？@Entity@Table(name = "stream")@SequenceGenerator(name = "sequence", sequenceName = "stream_id", allocationSize = 1)public class StreamEntity extends EntityWithId {    // @MappedSuperclass with ID     @Column(name = "request_id")    @OneToMany(            mappedBy = "streamEntity",            fetch = FetchType.LAZY    )    private List<RequestEntity> requestEntities = new ArrayList<>();    // getters setters}@Entity@Table(name = "request")@SequenceGenerator(name = "sequence", sequenceName = "request_id", allocationSize = 1, initialValue = 1)public class RequestEntity extends EntityWithId {    // @MappedSuperclass with ID     @JoinColumn(name = "stream_id")    @ManyToOne(fetch = FetchType.LAZY)    private StreamEntity streamEntity;    // getters setters}一些测试：@Testpublic void createStreamWithSeveralStreamTargetsAndDeleteStream() {    List<StreamEntity> streamEntities = createStream(1); // stream object is persisted here    List<RequestEntity> requestEntitySave = createRequest(1, streamEntityCheck);    assertEquals(1, requestEntitySave.size()); // request entity is persisted with the stream object into the database    List<StreamEntity> streamEntities = streamDao.findAll();    assertEquals(1, streamEntities.size());    StreamEntity streamEntity2 = streamEntities.get(0);    streamEntity2.getRequestEntities(); - this collection shows 0}我缺少什么？

Answer 1

由于一级缓存的概念，您创建并保存的初始对象与您加载的对象是同一个实例。由于您没有将创建的请求实体添加到内存模型中，而只是将其保存到数据库中，因此内存模型中不存在关系。

为了获得所需的结果，您需要清除保存和重新加载之间的持久性上下文。

@Test

    public void createStreamWithSeveralStreamTargetsAndDeleteStream() {

        List<StreamEntity> streamEntities = createStream(1); 

        List<RequestEntity> requestEntitySave = createRequest(1, streamEntityCheck);

        assertEquals(1, requestEntitySave.size()); 

        //you need to clear the persistence context here

        //now a db query should execute.

        //Inject the entitymanager to your test @PersistenceContext EntityManager em;

        em.clear();

        List<StreamEntity> streamEntities = streamDao.findAll();

        assertEquals(1, streamEntities.size());

        StreamEntity streamEntity2 = streamEntities.get(0);

        streamEntity2.getRequestEntities(); - this collection shows 0

   }