外鍵必須有相同數量爲多對一映射被引用的主鍵列

Question

嗨下面是我的實體，它們之間的關聯多對一

student.java

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

    @Id 
    @Column(name = "UserID") 
    private String userid; 

    @ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY) 
    @JoinColumns({ 
     @JoinColumn(name = "userrole", referencedColumnName = "VALUE"), 
     @JoinColumn(name = "userrole", referencedColumnName = "DESCRIPTION") 

    }) 
    private studentdetails userrole; 

//setters and getters 
//constructor 

} 

studentdetails.java

@Data 
@Entity 
@Table(name = "student_details") 
public class studentdetails { 

    @Id 
    @Column(name = "VALUE") 
    private String value; 

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

    //setters and getters 
    //constructor 
} 

appmain.java

public static void main() 
{ 

//session configuration 

studentdetails sd = new studentdetails(); 
sd.setvalue("abc"); 
sd.setdescription("abcdef"); 

student student1 = new student(); 
student.setuserid("1"); 
student.userrole(sd); 

student student2 = new student(); 
student.setuserid("2"); 
student.userrole(sd); 

session.save(student1); 
session.save(student2); 


} 

下面

都在我的2臺

student: 

UserID 
userrole 

student_details: 

VALUE 
DESCRIPTION 

在「student_details」應該進入學生表

的「UserRole的」「價值」，但是當我執行我的appmain我收到以下錯誤列

org.hibernate.MappingException: Foreign key (FK6D56043A4415BDB5:student [userrole])) must have same number of columns as the referenced primary key (student_details [VALUE,DESCRIPTION]) 
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:113) 
    at org.hibernate.mapping.ForeignKey.alignColumns(ForeignKey.java:96) 
    at org.hibernate.cfg.Configuration.secondPassCompileForeignKeys(Configuration.java:1354) 
    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1261) 
    at org.hibernate.cfg.AnnotationConfiguration.secondPassCompile(AnnotationConfiguration.java:383) 
    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1377) 
    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:954) 

我試圖解決這個問題，但它顯示同樣的錯誤 請建議我如何解決這個

Answer 1

要解決此問題，更改代碼：

@ManyToOne(cascade = CascadeType.ALL,fetch = FetchType.LAZY) 
    @JoinColumns({ 
     @JoinColumn(name = "userrole_value", referencedColumnName = "VALUE"), 
     @JoinColumn(name = "userrole_desc", referencedColumnName = "DESCRIPTION") 

    }) 
    private studentdetails userrole; 

原因問題：在映射：

@JoinColumns({ 
     @JoinColumn(name = "userrole", referencedColumnName = "VALUE"), 
     @JoinColumn(name = "userrole_desc", referencedColumnName = "DESCRIPTION") 

    }) 

你告訴Hibernate來創建Student實體表的外鍵被稱爲userrole指的是StudentDetails實體表中名爲VALUE的列。

然後在接下來的行中，您再次告訴休眠使用相同的柱面名稱 - userrole作爲FKey在StudentDetails中的列DESCRIPTION，所以此行覆蓋了前一個。

因此，hibernate會發現您試圖將單個列作爲外鍵在Student實體表中映射到StudentDetails實體表。但StudentDetails表具有由2列組成的複合鍵，因此hibernate會引發異常。

org.hibernate.MappingException: Foreign key (FK6D56043A4415BDB5:student [userrole])) must have same number of columns as the referenced primary key (student_details [VALUE,DESCRIPTION]) 

其他信息：

您試圖聲明一個複合的ID爲實體StudentDetails，所以這個實體應該implelemt Serializable接口，這是強制性的。 現在這個複合Id類應該覆蓋equals()和hashcode()方法。

只是一個建議，嘗試遵循您的實體和字段的Java命名約定。