[英]Why am I getting a LazyInitializationException when using FetchType.LAZY on one Set, but not on the other?
[英]ManyToOne FetchType.LAZY does not work. null always returned when getting the list
我正在使用 JPA 和 Spring 引導。 我有實體:
@Entity
public class Book {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(nullable = false, unique = true)
private String title;
@Column(nullable = false)
private String author;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "bookshelf_id", referencedColumnName = "id", nullable = true)
private Bookshelf bookshelf;
// getter & setter
}
@Entity
public class Bookshelf {
@Id
@GeneratedValue
private long id;
@Column(nullable = false)
private String location;
@OneToMany(mappedBy = "bookshelf", fetch = FetchType.LAZY)
private List<Book> books;
// getter & setter
}
然后在我的測試中,我嘗試檢索放在書架上的書:
Bookshelf shelf = new Bookshelf("room A");
Book book = new Book("a book", "chris");
book.setBookshelf(shelf);;
entityManager.persist(book);
entityManager.persist(shelf);
entityManager.flush();
Bookshelf persistedShelf = bookshelfRepository.findById(shelf.getId()).get();
Book persistedBook = bookRepository.findById(book.getId()).get();
book = null;
shelf = null;
shelf = persistedBook.getBookshelf();
int count = persistedShelf.getBooks().size();
assertEquals(1, count);
測試失敗,因為 getBooks() 總是在此行中返回 null:
int count = persistedShelf.getBooks().size();
測試日志顯示只執行了兩條 SQL 命令:
Hibernate: insert into bookshelf (location, id) values (?, ?)
Hibernate: insert into book (author, bookshelf_id, title, id) values (?, ?, ?, ?)
可能是什么問題?
嘗試設置從書架到書的反比關系:
Bookshelf shelf = new Bookshelf("room A");
Book book = new Book("a book", "chris");
book.setBookshelf(shelf);
// new code here:
List<Book> books = new ArrayList<>();
books.add(book);
shelf.setBooks(books);
entityManager.persist(book);
entityManager.persist(shelf);
entityManager.flush();
一般來說,您負責管理 JPA/Hibernate 中關系的雙方。
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