Mapping Extra Attribute in a Join Table JPA 2

Question

I am trying to model this relationship following this link http://www.javaworld.com/javaworld/jw-01-2008/images/datamodel.gif

Its the usual Many to Many relationship bet

Answer 1

There is no concept of having additional persistent attribute in relation in JPA (2.0). That's why relation with property is actually intermediate entity.

From both Order and Product entities, you need one-to-many relationship to new entity. Because of bidirectional relationship, new entity will have many-to-one relationships to Order and Product.

You need to go for something like this (shows only relationships, id's and other mappings stripped away):

@Entity
@Table(name="order_item")
public class OrderItem {
    @ManyToOne
    private Order order;
    @ManyToOne
    private Product product;
}

@Entity
public class Order {
    @OneToMany (mappedBy = "order")
    private Set<OrderItem> orderItems;
}

@Entity
public class Product {
    @OneToMany(mappedBy = "product")
    private Set<OrderItem> orderItems;
}