我對 Hibernate 很陌生，我已經在父對象和子對象之間設置了 @OneToMany 雙向關系，并期望當我將所有內容保留在數據庫中時，將父對象設置為子對象（因為子對象是關系的所有者）當我使用 ORM 獲取父對象時，我希望也獲取子對象，但作為回報，我看到零個子對象。據我在互聯網上閱讀的內容了解，當我將子對象保留為與父對象的關系的所有者時，完整的 ORM 應該發揮根據預定義關系映射連接兩個對象的魔力。此信息正確嗎？@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}一些測試：@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？
1 回答
寶慕林4294392
TA貢獻2021條經驗 獲得超8個贊
由于一級緩存的概念，您創建并保存的初始對象與您加載的對象是同一個實例。由于您沒有將創建的請求實體添加到內存模型中，而只是將其保存到數據庫中，因此內存模型中不存在關系。
為了獲得所需的結果，您需要清除保存和重新加載之間的持久性上下文。
@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
}
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