如何一次性保存父母和孩子（JPA和Hibernate）

我开始向你展示我的场景。

这是我的父对象：

@Entity
@Table(name="cart")
public class Cart implements Serializable{  

    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Id
    @Column(name="id")
    private Integer id; 

    @OneToMany(mappedBy="cart", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private List<CartItem> cartItems; 

    ...
}

这是我的子对象：

@Entity
@Table(name="cart_item")
public class CartItem implements Serializable{  

    @GeneratedValue(strategy=GenerationType.IDENTITY)   
    @Id
    @Column(name="id")
    private Integer id;     

    @ManyToOne
    @JoinColumn(name="cart_id", nullable=false)
    private Cart cart;

    ...
}

从数据库中可以看出，在表cart_item（子对象）中，字段cart_id具有表购物车（父对象）的字段 ID 的外键。

这是我保存对象的方式：

1） 有一个 restController 读取 JSON 对象：

@RestController
@RequestMapping(value = "rest/cart")
public class CartRestController {

    @Autowired
    private CartService cartService;    

    @RequestMapping(method = RequestMethod.POST)
    @ResponseStatus(value = HttpStatus.CREATED)
    public void create(@RequestBody CartDto cartDto) {
        cartService.create(cartDto);
    }
}

2）这是购物车服务，这只是一个接口：

public interface CartService {  
    void create(CartDto cartDto); 
}

这是 CartService 的实现：

import org.springframework.transaction.annotation.Transactional;

    @Service
    @Transactional
    public class CartServiceImpl implements CartService {   
        @Autowired
        private CartDao cartDao;

        @Override
        public void create(CartDto cartDto) {
            cartDao.create(cartDto);
        }
    }

CartDao只是另一个接口，我只向您展示它的实现：

@Repository
public class CartDaoImpl implements CartDao {

    @Autowired 
    private SessionFactory sessionFactory;

    // in this method I save the parent and its children
    @Override
    public void create(CartDto cartDto) {       

        Cart cart = new Cart(); 

        List<CartItem> cartItems = new ArrayList<>();                   

        cartDto.getCartItems().stream().forEach(cartItemDto ->{     
            //here I fill the CartItem objects;     
            CartItem cartItem = new CartItem();         
            ... 
            cartItem.setCart(cart);
            cartItems.add(cartItem);                
        });
        cart.setCartItems(cartItems);

        sessionFactory.getCurrentSession().save(cart);                  
    }
}

当我尝试保存新购物车及其cart_item时，我收到此错误：

SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/webstore] threw 
exception [Request processing failed; nested exception is 
org.springframework.orm.hibernate5.HibernateOptimisticLockingFailureException: Object of 
class     
[com.depasmatte.webstore.domain.CartItem] with identifier [7]: optimistic locking failed; 
nested exception is org.hibernate.StaleObjectStateException: Row was updated or deleted by 
another transaction (or unsaved-value mapping was incorrect) : 
[com.depasmatte.webstore.domain.CartItem#7]] with root cause
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction
 (or unsaved-value mapping was incorrect) : [com.depasmatte.webstore.domain.CartItem#7]

我想这个错误取决于这样一个事实，即当Hibernate尝试保存cart_item时，购物车的ID还不存在！

在拍摄时保存父对象及其子对象的正确方法是什么？谢谢