Multiple @ManyToOne fields pointing to same entity in JPA / Hibernate

Question

I have an Order entity that has a billingAddress and a shippingAddress . I also have an Address entity. I am trying to make a single address table hold both the shipping and billing addresses, since there is nothing to differentiate them, and the billing and shipping address can be the same in one or multiple orders. I have used @ManyToOne on the address fields in Order , but I'm not sure of the proper way to make this bidirectional.

I have two questions:

1. Is @ManyToOne appropriate for the address fields, since it is really an n:2 relationship that I simply am using two separate fields to represent? If not, what should I do instead?
2. Assuming 1. is OK, how do I make the mapping bidirectional (What annotation(s) should I use in the Address entity?)? Can this be done by listing multiple columns in an annotation in Address ?

Code:

@Entity
@Table(name = "orders")
public class Order {
  //...
    private Address shippingAddress;
    private Address billingAddress;

    @ManyToOne
    @JoinColumn(name = "shipping_address_id", referencedColumnName = "address_id", nullable = false)
    public Address getShippingAddress() {
        return shippingAddress;
    }

    @ManyToOne
    @JoinColumn(name = "billing_address_id", referencedColumnName = "address_id", nullable = false)
    public Address getBillingAddress() {
        return billingAddress;
    }
  //...
}

@Entity
@Table(name = "addresses")
public class Address {
    //address1, address2, city, state, etc.

    //how to link back to Orders?
    private Set<Order> orders;
}

Answer 1

Regarding your first question: is it a ManyToOne?

It depends. If several orders can have the same shipping address, then it's a ManyToOne. If only one order can have a given shipping address, then it's a OneToOne. Same for billing address.

I'm not sure making the association bidirectional is a good idea. I probably wouldn't do it in this case. But if you want to make it bidirectional, then you have to make them bidirectional. You indeed have two different associations here. The mapping would thus look like the following:

@OneToMany(mappedBy = "shippingAddress")
private Set<Order> shippedOrders;

@OneToMany(mappedBy = "billingAddress")
private Set<Order> billedOrders;

or, if the association is in fact a OneToOne (see answer to the first question):

@OneToOne(mappedBy = "shippingAddress")
private Order shippedOrder;

@OneToOne(mappedBy = "billingAddress")
private Order billedOrder;