Hibernate OneToOne关联

• 单向-共享主键

//Address不包含任何到User的信息
//使用optional=false，确定addr非空，这样hibernate不用检查addr是否为空，才能使用懒加载
//使用@PrimaryKeyJoinColumn使用Address的主键作为User的外键以及主键
//添加时需要先添加Address再添加User，并手动设置user.setId(addr.getId())
@Entity
class User{
  //不指定生成策略
  @Id
  private long id;
  @OneToOne(
  fetch = FetchType.LAZY,
  optional = false)
  @PrimaryKeyJoinColumn
  private Address addr;
}
//表结构
|       user               |address|
|id<pk><fk_from_address_id>|id|

• 双向-共享主键

@Entity
class User{
    @Id
    @GeneratedValue(generator = "addressKeyGenerator")
    @org.hibernate.annotations.GenericGenerator(
    name = "addressKeyGenerator",
    strategy = "foreign",
    parameters =
    @org.hibernate.annotations.Parameter(
            name = "property", value = "addr"
        )
    )
  private long id;
  @OneToOne(
  fetch = FetchType.LAZY,
  optional = false)
  @PrimaryKeyJoinColumn
  private Address addr;
}
@Entity
class Address{
    @Id
    @GeneratedValue
    private long id;
    @OneToOne(
    mappedBy = "addr",
    cascade = CascadeType.PERSIST)
    private User user;
}
//表结构
|       user               |address|
|id<pk><fk_from_address_id>|id|

• 不共享主键只要将@PrimarKeyJoinColumn改为@JoinColumn，并各自指定生成策略即可。

表结构
|  user  |address|
| id     | id |
|a_id<fk>| -  |

• 通过将@JoinColumn改为@JoinTable,可以使用关联表进行关联。

@Entity
public class Shipment {
  @OneToOne(fetch = FetchType.LAZY)
  @JoinTable(
    name = "ITEM_SHIPMENT",
    joinColumns = @JoinColumn(name = "SHIPMENT_ID"),
    inverseJoinColumns = @JoinColumn(
      name = "ITEM_ID",
      nullable = false,
      unique = true)
    )
  protected Item auction;
// ...
}