Spring boot JPA：在多对一关系中删除父实体时，如何保留子实体？

Question

我是Spring BootJPA的新手，正在努力找出多个实体之间的关系。

我有一个用户实体、一个产品实体和一个评论实体。一个用户有很多评论。一个产品有很多评论。评论有一个产品和一个用户。

目前，我正在为用户使用一对多的关系

我的问题：

1. 如何在不删除产品实体和用户实体的情况下删除审阅实体？
2. 我应该使用哪种级联类型？

用户实体：

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "user_name")
    private String userName;
    @Column(name = "email")
    private String email;
    @Column(name = "password")
    private String password;


    @JsonManagedReference("reviews")
    @JsonIgnore
    @OneToMany(fetch = FetchType.LAZY,
            mappedBy = "user")
    private List<Review> reviews = new ArrayList<>();
//constructor + getter+ setter

产品实体：

@Entity
@Table(name = "products")
public class Product {


    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Float price;
    @Transient
    private Float rate;

    private String category;
    private String brand;


    @JsonManagedReference("reviews")
    @JsonIgnore
    @OneToMany(mappedBy = "product")
    List<Review> reviews = new ArrayList<>();
//constructor + getter+ setter

审查实体:

@Entity
@Table(name = "reviews")
public class Review {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private Float rate;
    private String comment;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id",referencedColumnName = "id")
    @JsonBackReference("user")
    private User user;

    @ManyToOne(fetch = FetchType.LAZY)
    @JsonBackReference("product")
    @JoinColumn(name = "product_id",referencedColumnName = "id")
    private Product product;
//constructor + getter+ setter

用户控制器：

@CrossOrigin(origins = "http://localhost:3000")
@RestController
@RequestMapping(path="users/")
public class UserController {

    private final UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    ...
    @DeleteMapping("{userid}")
    public User deleteUser(@PathVariable("userid") Long userid){
        return userService.deleteById(userid);
    }
}

用户服务:

@Service
public class UserService {
    private final UserRepository userRepository;
    private final ReviewRepository reviewRepository;
    //dependency injection
    @Autowired
    public UserService(UserRepository userRepository, ReviewRepository reviewRepository) {
        this.userRepository = userRepository;
        this.reviewRepository =reviewRepository;
    }

   ...
    public User getUserById(Long id){
        return userRepository.findById(id).orElseThrow(()->
                new UserNotFoundException(id));
    }
    public User deleteById(Long id){
        User user = getUserById(id);
        userRepository.delete(user);
        return user;
    }

}

简单运行：

@SpringBootApplication
public class GroceryShoppingAppApplication  {

    public static void main(String[] args) {
        ConfigurableApplicationContext configurableApplicationContext =
                SpringApplication.run(GroceryShoppingAppApplication.class, args);

        UserRepository userRepository = configurableApplicationContext.getBean(UserRepository.class);
        ProductRepository productRepository =configurableApplicationContext.getBean(ProductRepository.class);
        ReviewRepository reviewRepository = configurableApplicationContext.getBean(ReviewRepository.class);

        User debbi= new User("Debbi","[e-mail]","password");

        Product apple = new Product("Apple",(float)3.40,"Fruit","Gala");
        Product milk = new Product("Milk",(float)5.22,"Dairy","Anchor");

        Review review1 = new Review(debbi,(float)4.5,"Good taste",apple);
        Review review2 = new Review(debbi,(float)5.0,"Good milk",milk);

        productRepository.save(apple);
        productRepository.save(milk);

        userRepository.save(debbi);

        reviewRepository.save(review1);
        reviewRepository.save(review2);

我认为我不应该使用casacadeType。所有这些都是因为当删除用户时，我不应该删除评论中的产品。我尝试了其他类型，错误仍然存在。因此，目前我没有使用任何casacadeType，需要逐个保存每个实体。

请帮我做这件事。

Answer 1

您会收到错误，因为审阅模型中的用户没有引用的列值。

请尝试以下代码：

@JoinCol列（name="user_id"，引用的列名="id"）