休眠 - @ManyToOne註釋創建額外的列

Question

因此，我正在關注一個關於hibernate的教程，因爲我想在即將推出的項目中使用該框架。我遇到了@ManyToOne和@OneToMay註釋和雙向映射的問題。我想要做的是非常基本的東西。我只想要兩張桌子，一張表示用戶，另一張表示車輛。現在，我希望用戶能夠擁有多輛車，並且汽車應該「知道」它所屬的用戶。

因爲它似乎是創建一個額外的表格，以保持用戶和車輛之間的連接的「最佳做法」。我試圖用@JoinTable註解（見下面）來做到這一點，但它不工作，因爲我想要它。

要做到這一點，我已經編寫了以下類：

UserDetails.java

​​3210

vehicle.java

@Entity 
public class Vehicle { 
@Id 
@GeneratedValue(strategy=GenerationType.IDENTITY) 
private int vehicleId; 
private String vehicleName; 
@ManyToOne 
private UserDetails user; 

... 
getters and setters 

和類檢驗以上：

HibernateTest.Java

public class HibernateTest { 
/** 
* 
* @param args 
*/ 
public static void main(String[] args){ 

    UserDetails user1 = new UserDetails();  
    user1.setUserName("testUser1"); 
    user1.setEmail("testEmail1"); 


    Vehicle vehicle1 = new Vehicle(); 
    vehicle1.setVehicleName("Car"); 

    Vehicle vehicle2 = new Vehicle(); 
    vehicle2.setVehicleName("Jeep"); 

    user1.getVehicle().add(vehicle1); 
    user1.getVehicle().add(vehicle2); 
    vehicle1.setUser(user1); 
    vehicle2.setUser(user1);  

    SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory(); 
    Session session = sessionFactory.openSession(); 
    session.beginTransaction(); 
    session.save(user1); 
    session.save(vehicle1); 
    session.save(vehicle2); 
    session.getTransaction().commit(); 
    session.close(); 

當我運行它，它的執行沒有任何錯誤或異常並創建下表：

USER_DETAILS 
+------+----------+---------+ 
|userId|email  |userName | 
+------+----------+---------+ 
|1  |testEmail1|testUser1| 
+------+----------+---------+ 

VEHICLE 
+---------+-----------+-----------+ 
|vehicleId|vehicleName|user_userId| <- did not expect this column 
+---------+-----------+-----------+ 
|1  |Car  |1   | 
+---------+-----------+-----------+ 
|2  |Jeep  |1   | 
+---------+-----------+-----------+ 

USER_VEHICLE 
+------+----------+ 
|USER_ID|VEHICLE_ID| 
+-------+----------+ 
|1  |1   | 
+-------+----------+ 
|1  |2   | 
+-------+----------+ 

據我瞭解，其他列「user_userId」這是由休眠創建的似乎是不必要的，因爲用戶和車輛之間的連接已經在「USER_VEHICLE」表中表示出來了，我不打算創建這個額外的列。

我做雙向映射的方式是錯誤的嗎？在沒有創建額外列的情況下，讓這個工作起作用的正確方法是什麼？

Answer 1

@JoinTable是必要的指定關係的，如果你想有一個@ManyToMany關係。

@Entity 
public class UserDetails { 
    /* ... */ 

    @ManyToMany 
    @JoinTable(name = "user_vehicle", 
     joinColumns = @JoinColumn(name = "user_id"), 
     inverseJoinColumns = @JoinColumn(name = "vehicle_id")) 
    private List<Vehicle> vehicles; 
} 

@Entity 
public class Vehicle { 
    /* ... */ 
} 

USER_DETAILS  VEHICLE   USER_VEHICLE 
+---------+  +------------+ +---------+------------+ 
| user_id |  | vehicle_id | | user_id | vehicle_id | 
+---------+  +------------+ +---------+------------+ 
|  1 |  |   1 | |  1 |   1 | 
+---------+  +------------+ +---------+------------+ 

---

既然你不想那些，你可以刪除@JoinTable像這樣：

@Entity 
public class UserDetails { 
    /* ... */ 

    @OneToMany(mappedBy = "user") 
    private List<Vehicle> vehicles; 
} 

@Entity 
public class Vehicle { 
    /* ... */ 

    @ManyToOne 
    private UserDetails user; 
} 

USER_DETAILS  VEHICLE  
+---------+  +------------+---------+ 
| user_id |  | vehicle_id | user_id | 
+---------+  +------------+---------+ 
|  1 |  |   1 |  1 | 
+---------+  +------------+---------+ 

---

你只需要第三個表，如果你想爲（UserDetails，Vehicle）元組存儲額外的數據，在這種情況下你會創建第三類。

@Entity 
public class UserDetails { 
    /* ... */ 

    @OneToMany(mappedBy = "user") 
    private List<UserVehicle> vehicles; 
} 

@Entity 
public class Vehicle { 
    /* ... */ 
} 

@Entity 
public class UserVehicle { 
    /* ... */ 

    @ManyToOne 
    private UserDetails user; 

    @ManyToOne 
    private Vehicle vehicle; 

    @Basic 
    private String someString; 
} 

USER_DETAILS  VEHICLE   USER_VEHICLE 
+---------+  +------------+ +---------+------------+-------------+ 
| user_id |  | vehicle_id | | user_id | vehicle_id | some_string | 
+---------+  +------------+ +---------+------------+-------------+ 
|  1 |  |   1 | |  1 |   1 | Hello  | 
+---------+  +------------+ +---------+------------+-------------+ 

Answer 2

這是列正常生成。數據庫關係中Many的一側必須保存FK值。

嘗試刪除您@Join註釋...只是@OneToMany

Answer 3

嘗試在Vehicle側和User端使用mapedBy財產