Hibernate OneToOne表聯接

Question

學習休眠。 我有以下類別的用戶，地區和國家，如下所示

     public class User {

     @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
     private int id;
     @Column(name = "first_name")
     Private String firstName;
     @Column(name = "last_name")
     private String lastName;
     @OneToOne(fetch = FetchType.EAGER)
     @JoinTable(name = "user_country_region", joinColumns ={@JoinColumn(name = "user_id") }, inverseJoinColumns = { @JoinColumn(name =   "country_id") })
     private Country userCountry;

     @OneToOne(fetch = FetchType.EAGER)
     @JoinTable(name = "user_country_region", joinColumns = {@JoinColumn(name = "user_id") }, inverseJoinColumns = { @JoinColumn(name = "region_id") })
     private Region userRegion;

     //With its respective Getters and Setters 
   }

    public class Country {

     @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
     private int id;
     @Column(name = "name")
     private String name;

     //With its respective Getters and Setters 
   }

   public class Region {

     @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
     private int id;
     @Column(name = "name")
     private String name;

     //With its respective Getters and Setters 
   }

面臨的問題是休眠查詢僅返回區域，而不返回國家。 是什么原因造成的？

嘗試獲取以下國家和地區值

    System.out.println("Country: "+user.getCountry().getName());
    System.out.println("Region: "+user.getRegion().getName());

來自Hibernate Show sql的響應。 似乎缺少國家/地區詳細信息。

    Hibernate: 
    select
       this_.id as id1_3_3_,
       this_.first_name as first_na2_3_3_,
       this_.last_name as last_na3_3_3_,
       region2_.id as id1_8_2_,
       region2_.name as name2_8_2_ 
    from
       user this_ 
    left outer join
       user_country_region this_1_ 
       on this_.id=this_1_.user_id  
    left outer join
    region region2_ 
       on this_1_.region_id=region2_.id 
    where
    this_.id=?

Answer 1

這是無效的映射。 我在通過Hibernate創建架構時遇到了Hibernate 5錯誤。

org.hibernate.boot.spi.InFlightMetadataCollector$DuplicateSecondaryTableException: 
Table with that name [user_country_region] already associated with entity

無論如何，如果您可以在您的Hibernate版本中使用此映射，則對於帶有兩個關系的聯接表進行此類映射很容易出錯。

只需使用此映射即可通過外鍵列將User與Country和Region相關聯。

public class User {

     @OneToOne
     private Country country;

     @OneToOne
     private Region region;

   }