对于一对一的双向映射，只需在子实体中定义@MapsId注释。

  @Entity 
 @Table（name =USER_DATA）
 public class UserData {

 @OneToOne（cascade = CascadeType.ALL，mappedBy =userData，orphanRemoval = true） 
私人实体实体; 

 public void setEntity（Entity entity）{
 this.entity = entity; 
 if（null！= entity&&& entity.getUserData（）！= this）{
 entity.setUserData（this）; 



 $ b @Entity 
 @Table（name =ENTITY）
公共类实体{

 @Id 
私人长ID; 

 @MapsId 
 @OneToOne 
 @JoinColumn（name =user_data_id）
 private UserData userData; 

 public void setUserData（UserData userData）{
 this.userData = userData; 
 if（null！= userData&&&& userData.getEntity（）！= this）{
 userData.setEntity（this）; 
} 
} 

} 
 

到许多单向映射，您必须使用@ElementalCollection和@CollectionTable，并使用@Embeddable注释来注释Entity.class

  @Entity 
 @Table（name =USER_DATA）
 public class UserData {

 @ElementCollection 
 @CollectionTable（name =entity，
 joinColumns = @ JoinColumn（name =user_data_id），
 uniqueConstraints = {@UniqueConstraint（columnNames 
 = {user_data_id，name}）}）
 private final Set< Entity> entities = new LinkedHashSet<>（）; 

 public void setEntities（Set< Entity> entities）{
 this.entities.clear（）; 
 if（null！= entities）{
 this.entities.addAll（entities）; 




可嵌入
公共类实体{

 @Column 
 @Access（ AccessType.FIELD）
私有字符串名称; 

} 
 

请参阅以下文章以加深理解： >
1.使用@PrimaryKeyJoinColumn共享主键的@OneToOne http://vard-lokkur.blogspot.my/2011/05/onetoone-with-shared-primary-key.html 。

2. @OneToOne使用@MapsId共享主键 http://vard-lokkur.blogspot.my/2014/05/onetoone-with-shared-primary-key.html

@Entity
@Table(name = "USER_DATA")
public class UserData {
    Entity entity;

    @OneToOne(fetch = FetchType.EAGER)
    @PrimaryKeyJoinColumn(name="PK_FK_ENTITY")
    @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})
    public Entity getEntity() {
        return entity;
    }

    public void setEntity(Entity entity) {
        this.entity = entity;
    }
}

Error given is "No identifier specified for entity". How can I specify that the entity field is both a primary and a foreign key? Note that there is no class hierarchy for 'UserData' here; it is just a single class. It just so happens that for every 'UserData' there will only be one 'Entity', hence we want to make it both a primary and a foreign key.

For one to one bidirectional mapping, just define the @MapsId annotation at the child entity.

@Entity
@Table(name = "USER_DATA")
public class UserData {

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "userData", orphanRemoval = true)
    private Entity entity;

    public void setEntity(Entity entity) {
        this.entity = entity;
        if (null != entity && entity.getUserData() != this) {
            entity.setUserData(this);
        }
    }
}

@Entity
@Table(name = "ENTITY")
public class Entity {

    @Id
    private Long id;

    @MapsId
    @OneToOne
    @JoinColumn(name = "user_data_id")
    private UserData userData;

    public void setUserData(UserData userData) {
        this.userData = userData;
        if (null != userData && userData.getEntity() != this) {
            userData.setEntity(this);
        }
    }

}

For one to many unidirectional mapping, You have to use @ElementalCollection and @CollectionTable and annotate Entity.class with @Embeddable annotation

        @Entity
        @Table(name = "USER_DATA")
        public class UserData {

             @ElementCollection
             @CollectionTable(name = "entity", 
                              joinColumns = @JoinColumn(name = "user_data_id"), 
                              uniqueConstraints = { @UniqueConstraint(columnNames     
= { "user_data_id", "name" }) })
             private final Set<Entity> entities = new LinkedHashSet<>();

             public void setEntities(Set<Entity> entities) {
                 this.entities.clear();
                 if (null != entities) {
                     this.entities.addAll(entities);
                 }
             }
        }

        @Embeddable
        public class Entity {

            @Column
            @Access(AccessType.FIELD)
            private String name;

        }

Kindly refers to the following articles for better understanding:
1. @OneToOne with shared primary key using @PrimaryKeyJoinColumn http://vard-lokkur.blogspot.my/2011/05/onetoone-with-shared-primary-key.html.

2. @OneToOne with shared primary key using @MapsId http://vard-lokkur.blogspot.my/2014/05/onetoone-with-shared-primary-key.html