Issues with @ManyToMany hibernate mapping

Question

I am new to web development. I have been trying to make an e commerce platform and using @ManyToMany mapping between product and wishlist using wishlist_product as the joining table.

Upon adding, I am not facing error, but the data is not been added in the join table. I have been trying to resolve this issue for 2 days now, but have been facing continuous failure. I have attached the code for both, wishlist and product below.

@Entity
@Table(name = "wishlist")
public class Wishlist {

    @Id
    @Column(name = "username")
    /*
     * @GeneratedValue(generator = "gen")
     * 
     * @GenericGenerator(name = "gen", strategy = "foreign", parameters
     * = @Parameter(name = "property", value = "login"))
     */
    private String username;

    @ManyToMany
    @JoinTable(name = "wishlist_product", 
                joinColumns = @JoinColumn(name = "username"),
                inverseJoinColumns = @JoinColumn(name = "product_id"))
    private List<Electronics> product;

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@Table(name = "electronics")
@DiscriminatorColumn(name = "product_Type", discriminatorType = DiscriminatorType.STRING)
public class Electronics {

    @Id
    @GenericGenerator(name = "CamIdGenerator", strategy = "com.virtusa.neuralhack.vlx.IdGenerator.CameraIdGenerator")
    @GeneratedValue(generator = "CamIdGenerator")
    // @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "product_id")
    private String productId;

    private String askingPrice;

    @Column(name = "age")
    private String howOld;

    @Column(name = "model")
    private String model;

    @Column(name = "brand")
    private String brand;

    @Column(name = "description")
    private String description;

    transient private String email;

    @ManyToOne
    @JoinColumn(name = "username")
    private User_Login user;

    @ManyToMany
    @JoinTable(name = "wishlist_product", joinColumns = @JoinColumn(name = "product_id"), inverseJoinColumns = @JoinColumn(name = "username"))
    private List<Wishlist> wishlist;

public void addToWishlist(String email, String productId) {

    Session currentSession = manager.unwrap(Session.class);
    Wishlist wishlist = currentSession.get(Wishlist.class,email);
        
    //System.out.println(wishlist.getUser());
        
    Electronics product = currentSession.get(Electronics.class, productId);
    System.out.println(product);

    wishlist.addToWishlist(product);
        
    //product.addAWishlist(wishlist);
    //System.out.println(wishlist.getProduct().get(0));

    currentSession.saveOrUpdate(wishlist);
}

Answer 1

Make sure you in the read-write transaction but not read-only.

And some advises:

• do not use the cascade = CascadeType.ALL with the many-to-many association due to CascadeType.ALL includes CascadeType.REMOVE that in the case of many-to-many leads to too many entities are removed
• use Set instead of List for to-many association when you don't need specific order.