Hibernate OneToOne關聯

• 單向-共享主鍵

//Address不包含任何到User的信息
//使用optional=false，確定addr非空，這樣hibernate不用檢查addr是否爲空，才能使用懶加載
//使用@PrimaryKeyJoinColumn使用Address的主鍵作爲User的外鍵以及主鍵
//添加時需要先添加Address再添加User，並手動設置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;
}
//表結構
|       user               |address|
|id<pk><fk_from_address_id>|id|

• 雙向-共享主鍵

@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;
}
//表結構
|       user               |address|
|id<pk><fk_from_address_id>|id|

• 不共享主鍵只要將@PrimarKeyJoinColumn改爲@JoinColumn，並各自指定生成策略即可。

表結構
|  user  |address|
| id     | id |
|a_id<fk>| -  |

• 通過將@JoinColumn改爲@JoinTable,可以使用關聯表進行關聯。

@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;
// ...
}