Spring boot JPA: How to keep the child entity when deleting the parent entity in a many-to-one relationship?

Question

I'm new to the Spring boot JPA and struggling to find out the relationships between multiple entities.

I have a User Entity, a Product Entity, and a Review Entity. A user has many reviews. A product has many reviews. A review has a product and a user.

At the moment, I'm using one-to-many relationships for user&reivew, product&review. However, the error occurred when deleting a review: ERROR: update or delete on table "users" violates foreign key constraint "fkcgy7qjc1r99dp117y9en6lxye" on table "reviews".

My question:

1. How can I delete a Review Entity without deleting the Product entity and User entity?
2. Which cascade type should I use?

---

User Entity:

@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

Product Entity:

@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

Review Entity:

@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")
    @JsonBackReference("user")
    private User user;

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

User Controller:

@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);
    }
}

User service:

@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;
    }

}

Simple run:

@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","debbi@gamil.com","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);

I think I should not use casacadeType.All because when deleting a user, I shouldn't delete the product in the review. I tried other types, the error still remains. Thus, currently I didn't use any casacadeType and need to save each entity one by one.

Please help me with this.

Answer 1

You are getting an error because the user in the review model does not have a referenced Column value.

Try this code:

@JoinColumn(name = "user_id",referencedColumnName = "id")