我有两个例子,首先是@OneToOne单向映射和第二个双向.在单向映射中,拥有端表必须包含引用其他表的id的连接列;那么在双向中,它们之间必须包含彼此的外键列.但是在使用自动生成策略生成数据库模式之后,两个示例对数据库模式具有相同的效果.单向映射是正常的,但双向示例只包含一个外键列,但它必须涉及彼此的外键！
单向映射
@Entity
public class Customer43 {
@Id
@GeneratedValue
private Long id;
private String firstName;
private String lastName;
private String email;
private String phoneNumber;
@OneToOne
@JoinColumn(name = "address_fk")
private Address43 address;
// Getters,Setters and Constructors.
}
@Entity
public class Address43 {
@Id
@GeneratedValue
private Long id;
private String street1;
private String street2;
private String city;
private String state;
private String zipcode;
private String country;
// Getters,Setters and Constructors.
}
双向映射
@Entity
public class Customer44 {
@Id
@GeneratedValue
private Long id;
private String firstName;
private String lastName;
private String email;
private String phoneNumber;
@OneToOne
@JoinColumn(name = "address_fk")
private Address43 address;
// Getters,Setters and Constructors.
}
@Entity
public class Address44 {
@Id
@GeneratedValue
private Long id;
private String street1;
private String street2;
private String city;
private String state;
private String zipcode;
private String country;
@OneToOne(mappedBy = "address")
private Customer44 customer;
// Getters,Setters and Constructors.
}
解决方法
因为您不了解双向OneToOne的映射方式.你不需要两个外键.一个单独的一个足以在两个方向上执行两个表之间的连接：
select a.* from address a inner join customer c on c.addressId = a.id; select c.* from customer c inner join address a on c.addressId = a.id;
关联是单向或双向的事实不会改变表如何链接在一起.它只是更改映射,并允许在两个方向上导航关联.
在双向关联中,您始终拥有一个拥有方(它告诉关联如何映射,使用哪个连接列)和一个反面,您只需说：我是该对象映射的对方字段(mappingBy属性值中的字段).
