ManyToMany JoinTable issue

kehnkis · **Joined:** Thu Feb 14, 2008 6:51 am **Posts:** 1

Hi,

I have a ManyToMany relation between a Product and Order class for a eCommerce application :

Product :

Code:

@Entity
@Table(name="PRODUCTS")
public class Product implements Serializable{
   
   @Id
   @GeneratedValue(strategy=GenerationType.AUTO)
   private int productId;
   private float price;
   private String brand;
   private int quantity;
   
   @ManyToMany(mappedBy="products")
   private List<Order> orders;
        ...
}

Order :

Code:

@Entity
@Table(name="ORDERS")
public class Order implements Serializable{
   
   private static final long serialVersionUID = 1L;

   @Id
   @GeneratedValue(strategy=GenerationType.AUTO)
   private int orderId;
   
   @ManyToMany(fetch=FetchType.EAGER)
   @Fetch(FetchMode.SUBSELECT)
     @JoinTable(name="OrdersProducts", 
              joinColumns=@JoinColumn(name="orderId",           referencedColumnName="orderId"), 
              inverseJoinColumns=@JoinColumn(name="productId", referencedColumnName="productId") )
         
   private List<Product> products;
 
        .....

It works fine, but in my join table I only have the productId and orderId, I would like to have a "quantity" field. Is it possible to map a new field in a join table with an attribute from a collection ? Or is there a pattern to handle my problem ?

Thanx
Best regards,

John

JumBay · **Joined:** Thu Feb 14, 2008 11:40 am **Posts:** 1

Hi,

hum... I think that is possible, and I will be interested too but I don't know how to do that.

I hope someone will figure it out.

gchawla · **Joined:** Thu Feb 14, 2008 2:36 pm **Posts:** 2

I would also like to know this and would also be interested in finding out from experts on How to create a primary key on the join table ( using annotations) ?

Regards

anirudhvyas010 · **Joined:** Thu Dec 13, 2007 2:32 pm **Posts:** 26

Create a Join table class like in this case ProductOrder;

create an inner Id class (static) if you have composite Id ( i.e. Primary key(id_1, id_2) ), then in the containing class ( that is class that contains Id, which here is ProductOrder ) declare the fields as you see fit.

ProductOrder has MANY-TO-ONE association with Product and MANY-TO-ONE association with Order, so you would have that in your mapping files as well as in your ProductOrder class, just make sure that you manage foreign key relationships neatly.

I can give an example, but if you have JP with Hibernate, theres an example like that given, you can refer to it.

Regards
Vyas,Anirudh

gchawla · **Joined:** Thu Feb 14, 2008 2:36 pm **Posts:** 2

Hi ,
Can you please give an example ?

MarkHolmes · **Joined:** Tue Feb 19, 2008 10:25 pm **Posts:** 5

This is modified from listing 7.1, pg 304, in Java Persistence with Hibernate...

Code:

@Entity
@Table(name="ordered_lines")
public class OrderLine
{
    @Embeddable
    public static class Id
        implements Serializable
    {
        @Column(name="order_id")
        private Long orderId;

        @Column(name="product_id")
        private Long productId;

        public Id() {}

        public Id(Long orderId, Long productId)
        {
            this.orderId = orderId;
            this.productId = productId;
        }

        public boolean equals(Object o)
        {
            // compare this and that Id properties (orderIds and productIds)
        }

        public int hashCode() {
            // add the orderId and productId hashCode()s
        }
    }

    @EmbeddedId
    private Id id = new Id();

    @ManyToOne
    @JoinColumn(
        name="order_id",
        insertable="false",
        updatable="false"
    )
    private Order order;

    @ManyToOne
    @JoinColumn(
        name="product_id",
        insertable="false",
        updatable="false"
    )
    private Product product;

    // create attributes you want to save in the join table

    public OrderedLine() {}

    public OrderedLine(
        Order order,
        Product product
        /* other attributes */)
    {
        this.id.orderId = order.getId();
        this.id.productId = product.getId();

        // these are two one-to-many relationships mapped
        // one in each of Order and Product
        order.getOrderLines().add(this);
        order.getOrderLines().add(this);

        // set other attributes
    }

    // accessor methods
}

anirudhvyas010 · **Joined:** Thu Dec 13, 2007 2:32 pm **Posts:** 26

read my this post for the example ( the only thing that is missing from the mapping was cascade="save-update" from ProductParts table

http://forum.hibernate.org/viewtopic.php?t=983932