Hibernate/JPA中@OneToOne和@MapsId的使用

双向@OneToOne的效率低于与父表共享主键的单向@OneToOne。因此，不要使用双向@OneToOne，最好是依靠单向@OneToOne和@MapsId。第一步：在子实体这边使用@MapsId基本上，上面@OneToOne关联，它将与父表共享主键，父实体见如下，父实体中没有@OneToOne，这说明是从子实体指向父实体的单向关联；

第一步：在子实体这边使用@MapsId： 

 

@Entity
public class Book implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @NotNull
    @Column(name = "title", nullable = false)
    private String title;

    @Column(name = "description")
    private String description;

    @Column(name = "publication_date")
    private LocalDate publicationDate;

    @Column(name = "price", precision = 21, scale = 2)
    private BigDecimal price;

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private Author author;

基本上，上面@OneToOne关联，它将与父表共享主键，父实体见如下，父实体中没有@OneToOne，这说明是从子实体指向父实体的单向关联： 

@Entity
public class Author implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "birth_date")
    private LocalDate birthDate;