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[英]One-to-many hierarchy object structure not getting persisted on using hibernate
[英]Getting the ID of the persisted child object in a one-to-many relationship
我有兩個實體類A和B,如下所示。
public class A{
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@OneToMany(mappedBy = "a", fetch = FetchType.LAZY, cascade = {CascadeType.ALL})
private List<B> blist = new ArrayList<B>();
//Other class members;
}
B級:
public class B{
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@ManyToOne
private A a;
//Other class members;
}
我有一個方法,它將B對象添加到A對象。 我想返回新添加的B對象的id。
例如:
public Long addBtoA(long aID){
EntityTransaction tx = myDAO.getEntityManagerTransaction();
tx.begin();
A aObject = myDAO.load(aID);
tx.commit();
B bObject = new B();
bObject.addB(bObject);
tx.begin();
myDAO.save(aObject);
tx.commit();
//Here I want to return the ID of the saved bObject.
// After saving aObject it's list of B objects has the newly added bObject with it's id.
// What is the best way to get its id?
}
我有一個方法,它將B對象添加到A對象。 我想返回新添加的B對象的id。
那就做吧! 在保留新B實例(並且已更改刷新到數據庫)之后,已分配其id
,只需返回它。 這是一個說明此行為的測試方法:
@Test
public void test_Add_B_To_A() {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("MyPu");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin();
A a = em.find(A.class, 1L);
B b = new B();
A.addToBs(b); // convenient method that manages the bidirectional association
em.getTransaction().commit(); // pending changes are flushed
em.close();
emf.close();
assertNotNull(b.getId());
}
順便說一句,你的代碼有點亂,你不需要在每次與EM交互后commit
。
我不認為接受的答案是正確的。 請參閱https://coderanch.com/t/628230/framework/Springwel-obtain-id-added
tldr; 您應該只為子B
創建一個存儲庫,這樣您就可以完全獨立於父級保存子級。 獲得保存的B entity
后,將其與其父A
關聯。
下面是一些示例代碼,其中Todo
是父級,而Comment
是孩子。
@Entity
public class Todo {
@OneToMany(mappedBy = "todo", cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
private Set<Comment> comments = new HashSet<>();
// getters/setters omitted.
}
@Entity
public class Comment {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@ManyToOne
@JoinColumn(name = "todo_id")
private Todo todo;
// getters/setters omitted.
}
如果這是在spring數據中建模的,則創建2個存儲庫。 TodoRepository
和CommentRepository
這是Autowired
英寸
給定一個休息端點,能夠接收POST /api/todos/1/comments
以將新評論與給定的待辦事項ID相關聯。
@PostMapping(value = "/api/todos/{todoId}/comments")
public ResponseEntity<Resource<Comment>> comments(@PathVariable("todoId") Long todoId,
@RequestBody Comment comment) {
Todo todo = todoRepository.findOne(todoId);
// SAVE the comment first so its filled with the id from the DB.
Comment savedComment = commentRepository.save(comment);
// Associate the saved comment to the parent Todo.
todo.addComment(savedComment);
// Will update the comment with todo id FK.
todoRepository.save(todo);
// return payload...
}
相反,如果您執行了以下操作並保存了提供的參數comment
。 獲取新注釋的唯一方法是遍歷todo.getComments()
並查找提供的comment
,如果集合是Set
則該comment
很煩人且不切實際。
@PostMapping(value = "/api/todos/{todoId}/comments")
public ResponseEntity<Resource<Comment>> comments(@PathVariable("todoId") Long todoId,
@RequestBody Comment comment) {
Todo todo = todoRepository.findOne(todoId);
// Associate the supplied comment to the parent Todo.
todo.addComment(comment);
// Save the todo which will cascade the save into the child
// Comment table providing cascade on the parent is set
// to persist or all etc.
Todo savedTodo = todoRepository.save(todo);
// You cant do comment.getId
// Hibernate creates a copy of comment and persists it or something.
// The only way to get the new id is iterate through
// todo.getComments() and find the matching comment which is
// impractical especially if the collection is a set.
// return payload...
}
您應該先保留新創建的對象,然后將其添加到其容器中。 另外, org.hibernate.Session
的save
方法返回一個新持久化對象的標識符。 所以你只需更新你的代碼和/或你的DAO就像這樣:
newObject.setContainer(container); // facultative (only if the underlying SGBD forbids null references to the container)
Long id = (Long) hibernateSession.save(newObject); // assuming your identifier is a Long
container.add(newObject);
// now, id contains the id of your new object
無論如何,對於生成id的所有對象,您總是可以執行以下操作:
hibernateSession.persist(object); // persist returns void...
return object.getId(); // ... but you should have a getId method anyway
如果有人在先前的評論中找不到解決方案,則另一個選項是添加
@GeneratedValue(strategy = yourChosenStrategy)
在你持久存在的實體的ID上(或在它的getter上)。 在這種情況下,當調用persist時,id將自動設置在持久化對象中。
希望能幫助到你 !
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