How to implement OneToMany communication?

Question

Hibernate

I have a product class:

@Entity
public class Product {

    set<Category> categories;
}

And I need to link it somehow to the category

@Entity
public class Category {
   //...
}

However, when deleting a product, the categories associated with it should not be deleted. And vice versa. When deleting a category, products should remain in the database, and Set should immediately be updated (become one category less). How to implement it?

Answer 1

@Table(name="parent")
class Parent {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
 
    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
    private Set<Child> attachments = new HashSet<Child>();
    .....
}
 
@Entity
@Table(name="child)
class Child {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
 
    @ManyToOne
    @JoinColumn(name = "parent_id", nullable = false)
    private Parent parent;
    ...
}

@Entity