尝试更新整个对象时出现TransientObjectException

@Entity
public class Parent {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToOne(cascade = CascadeType.ALL)
    private Child child;

    // getters and setters
}

@Entity
public class Child {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    // other fields, getters and setters
}

// 在服务层
public void saveParentWithChild(Parent parent) {
    entityManager.persist(parent.getChild()); // 先保存子对象
    entityManager.persist(parent); // 再保存父对象
}

@OneToOne(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
private Child child;

if (!entityManager.contains(parent) || entityManager.getEntityManagerFactory().getPersistenceUnitUtil().isLoaded(parent) && parent.getId() == null) {
    throw new IllegalStateException("Parent object is transient or already deleted.");
}

@Entity
public class Author {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    // getters and setters
}

@Entity
public class Post {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String content;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "author_id")
    private Author author;

    // getters and setters
}

// 在服务层
public void savePostWithAuthor(Post post) {
    if (post.getAuthor() != null && post.getAuthor().getId() == null) {
        entityManager.persist(post.getAuthor()); // 先保存作者
    }
    entityManager.persist(post); // 再保存帖子
}