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;
// ...
}