带有主键的Hibernate类也是外键 [英] Hibernate class with primary key that is also a foreign key

问题描述

  @Entity 
 @Table（name =USER_DATA）
 public class UserData {
实体实体; 
 
 @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; 
 
 
 
 
 
 
给出的错误是没有为实体指定标识符。我如何指定实体字段既是主键又是外键？请注意，这里没有'UserData'的类层次结构;它只是一个班级。对于每个'UserData'来说，只会有一个'Entity'，因此我们希望将它同时作为主键和外键。 
 
解决方案
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 。
 
 
 @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.
解决方案
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.

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


                        
这篇关于带有主键的Hibernate类也是外键的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！