Hibernate Mapping - Joining two tables with an ass

问题:

I have the following entities... Customer, Card and Address

Customer:

 {
     private String cust_id; // Primary key
     .....

     @OneToOne
     Address address; // I want to load address of the customer. 
                      // Can change the association to @OneToMany, if needed
 }

Card:

 {
    private String card_id; // Primary Key
    private String cust_id; // Foreign Key to Customer.cust_id
    ....
 }

Address:

 {
    private String card_id; // Foreign key to card.card_id
    private String address1;
    .....
 }

When I load customers I want to load Addresses with association table Card. But the tricky part is Address does not have a primary key. It only has a Foreign key.

回答1:

You could use the annotation @JoinTable after the @OneToOne to point the card's table, so you won't need an entity for card, but if the card's table isn't just a relational table, you could map card in User as @OneToOne and have a @Transient 'getAddress()' method that returns 'this.card.getAddress()', but on card's entity you must map the relation between Address and Card(@OneToOne(mappedBy='card_id')), and in Address you could map card_id as @Id.

First Alternative

Customer:

@OneToOne
@JoinTable(name="card", joinColumns = @JoinColumn(name="cust_id"),
inverseJoinColumns = @JoinColumn(name="card_id"))
private Address address;

Second alternative

Customer:

@OneToOne(mappedBy="cust_id")
private Card card;

...
@Transient
public Address getAddress(){
 return this.card == null ? null : this.card.getAddress();
}

Card:

@OneToOne(mappedBy="card_id")
private Address address;

Address:

@Id
private String card_id;

In the Second case Card has a Embedded pk which is formed by two fks(Customer and Address)

Card:

@EmbeddedId
private CustomerAddressPK id;

CustomerAddressPK

@Embeddable
public class CustomerAddressPK(){

  private String cust_id;
  private String card_id;
}

回答2:

The mapping between Customer and Address can be made by using the concept of Dependent objects.

Look at the documentation, you will find similar example where there is a mapping between Person entity with dependent object called Name.